U.S. patent application number 17/666984 was filed with the patent office on 2022-05-26 for radio wave absorbing composition and radio wave absorber.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Hirokazu Hashimoto, Yoshihiro NAKAI.
Application Number | 20220166147 17/666984 |
Document ID | / |
Family ID | 1000006185063 |
Filed Date | 2022-05-26 |
United States Patent
Application |
20220166147 |
Kind Code |
A1 |
NAKAI; Yoshihiro ; et
al. |
May 26, 2022 |
RADIO WAVE ABSORBING COMPOSITION AND RADIO WAVE ABSORBER
Abstract
There is provided a radio wave absorbing composition containing
a magnetic powder and a binder. There is also provided a radio wave
absorber containing a magnetic powder and a binder. The magnetic
powder is a powder of a substitution-type hexagonal ferrite
subjected to surface treatment with a surface treatment agent, the
surface treatment agent is a silicon-based compound, and the binder
is an olefin-based resin.
Inventors: |
NAKAI; Yoshihiro;
(Minami-ashigara-shi, JP) ; Hashimoto; Hirokazu;
(Minami-ashigara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
1000006185063 |
Appl. No.: |
17/666984 |
Filed: |
February 8, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2020/029625 |
Aug 3, 2020 |
|
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17666984 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 9/0083 20130101;
C01G 49/009 20130101; C08K 9/06 20130101; H05K 9/0075 20130101;
H01Q 17/004 20130101; C01G 49/0036 20130101 |
International
Class: |
H01Q 17/00 20060101
H01Q017/00; H05K 9/00 20060101 H05K009/00; C01G 49/00 20060101
C01G049/00; C08K 9/06 20060101 C08K009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 9, 2019 |
JP |
2019-148186 |
Claims
1. A radio wave absorbing composition comprising: a magnetic
powder; and a binder, wherein the magnetic powder is a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent, the surface treatment agent is a
silicon-based compound, and the binder is an olefin-based
resin.
2. The radio wave absorbing composition according to claim 1,
wherein the substitution-type hexagonal ferrite has a constitution
represented by General Formula 1, AFe.sub.(12-x)Al.sub.xO.sub.19
General Formula 1: in General Formula 1, A represents one or more
kinds of atoms selected from the group consisting of Sr, Ba, Ca,
and Pb, and x satisfies 1.50.ltoreq.x.ltoreq.8.00.
3. The radio wave absorbing composition according to claim 1,
wherein the substitution-type hexagonal ferrite is a
substitution-type hexagonal strontium ferrite.
4. The radio wave absorbing composition according to claim 1,
wherein the surface treatment agent is a silicon-based compound
represented by General Formula 2, (X-L).sub.m-Si--Z.sub.4-m General
Formula 2: in General Formula 2, X represents a hydrogen atom, an
alkyl group, an alkenyl group, an aryl group, an alicyclic group, a
heterocyclic group, a hydroxy group, an acrylamide group, a
sulfanyl group, an isocyanate group, a thiocyanate group, a ureido
group, a cyano group, an acid anhydride group, an azide group, a
carboxy group, an acyl group, a thiocarbamoyl group, a phosphate
group, a phosphanyl group, a sulfonic acid group, or a sulfamoyl
group, L represents one divalent group or one bond, selected from
the group consisting of a single bond, an alkylene group, an
alkenylene group, an alkynylene group, an arylene group, --O--,
--S--, --NR.sup.a--, an ester bond, a thioester bond, an amide
bond, a thioamide bond, and a sulfonyl group, or a divalent group
or a bond, obtained by combining two or more of these, R.sup.a
represents a hydrogen atom or a substituent, Z represents a hydroxy
group, an alkoxy group, or an alkyl group, and m is an integer in a
range of 1 to 3.
5. The radio wave absorbing composition according to claim 4,
wherein in General Formula 2, m is 1, and X represents an alkenyl
group or a heterocyclic group, or m is 2 or 3, and a plurality of
X's included in General Formula 2 each independently represent an
alkenyl group or a heterocyclic group.
6. The radio wave absorbing composition according to claim 4,
wherein in General Formula 2, m is 1, and X represents an acyl
group, an acrylamide group, or a heterocyclic group, or m is 2 or
3, and a plurality of X's included in General Formula 2 each
independently represent an acyl group, an acrylamide group, or a
heterocyclic group, where the acyl group is a (meth)acryloyl group,
and the heterocyclic group is an epoxy group.
7. The radio wave absorbing composition according to claim 4,
wherein in General Formula 2, X represents a heterocyclic group,
and the heterocyclic group is an epoxy group.
8. The radio wave absorbing composition according to claim 7,
wherein in General Formula 2, L includes an alkylene group having 4
to 12 carbon atoms.
9. The radio wave absorbing composition according to claim 1,
wherein the olefin-based resin is one or more resins selected from
the group consisting of polyethylene, polypropylene,
polymethylpentene, an ethylene-vinyl acetate resin, a cycloolefin
resin, and an olefin-based resin containing a maleic acid anhydride
unit.
10. The radio wave absorbing composition according to claim 1,
wherein the olefin-based resin is one or more resins selected from
the group consisting of polymethylpentene, a cycloolefin resin, and
an olefin-based resin containing a maleic acid anhydride unit.
11. A radio wave absorber comprising: a magnetic powder; and a
binder, wherein the magnetic powder is a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent, the surface treatment agent is a
silicon-based compound, and the binder is an olefin-based
resin.
12. The radio wave absorber according to claim 11, wherein the
substitution-type hexagonal ferrite has a constitution represented
by General Formula 1, AFe.sub.(12-x)Al.sub.xO.sub.19 General
Formula 1: in General Formula 1, A represents one or more kinds of
atoms selected from the group consisting of Sr, Ba, Ca, and Pb, and
x satisfies 1.50.ltoreq.x.ltoreq.8.00.
13. The radio wave absorber according to claim 11, wherein the
substitution-type hexagonal ferrite is a substitution-type
hexagonal strontium ferrite.
14. The radio wave absorber according to claim 11, wherein the
surface treatment agent is a silicon-based compound represented by
General Formula 2, (X-L).sub.m-Si--Z.sub.4-m General Formula 2: in
General Formula 2, X represents a hydrogen atom, an alkyl group, an
alkenyl group, an aryl group, an alicyclic group, a heterocyclic
group, a hydroxy group, an acrylamide group, a sulfanyl group, an
isocyanate group, a thiocyanate group, a ureido group, a cyano
group, an acid anhydride group, an azide group, a carboxy group, an
acyl group, a thiocarbamoyl group, a phosphate group, a phosphanyl
group, a sulfonic acid group, or a sulfamoyl group, L represents
one divalent group or one bond, selected from the group consisting
of a single bond, an alkylene group, an alkenylene group, an
alkynylene group, an arylene group, --O--, --S--, --NR.sup.a--, an
ester bond, a thioester bond, an amide bond, a thioamide bond, and
a sulfonyl group, or a divalent group or a bond, obtained by
combining two or more of these, R.sup.a represents a hydrogen atom
or a substituent, Z represents a hydroxy group, an alkoxy group, or
an alkyl group, and m is an integer in a range of 1 to 3.
15. The radio wave absorber according to claim 14, wherein in
General Formula 2, m is 1, and X represents an alkenyl group or a
heterocyclic group, or m is 2 or 3, and a plurality of X's included
in General Formula 2 each independently represent an alkenyl group
or a heterocyclic group.
16. The radio wave absorber according to claim 14, wherein in
General Formula 2, m is 1, and X represents an acyl group, an
acrylamide group, or a heterocyclic group, or m is 2 or 3, and a
plurality of X's included in General Formula 2 each independently
represent an acyl group, an acrylamide group, or a heterocyclic
group, where the acyl group is a (meth)acryloyl group, and the
heterocyclic group is an epoxy group.
17. The radio wave absorber according to claim 14, wherein in
General Formula 2, X represents a heterocyclic group, and the
heterocyclic group is an epoxy group.
18. The radio wave absorber according to claim 17, wherein in
General Formula 2, L includes an alkylene group having 4 to 12
carbon atoms.
19. The radio wave absorber according to claim 11, wherein the
olefin-based resin is one or more resins selected from the group
consisting of polyethylene, polypropylene, polymethylpentene, an
ethylene-vinyl acetate resin, a cycloolefin resin, and an
olefin-based resin containing a maleic acid anhydride unit.
20. The radio wave absorber according to claim 11, wherein the
olefin-based resin is one or more resins selected from the group
consisting of polymethylpentene, a cycloolefin resin, and an
olefin-based resin containing a maleic acid anhydride unit.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of PCT International
Application No. PCT/JP2020/029625 filed on Aug. 3, 2020, which
claims priority under 35 U.S.C. .sctn. 119(a) to Japanese Patent
Application No. 2019-148186 filed on Aug. 9, 2019. Each of the
above applications is hereby expressly incorporated by reference,
in its entirety, into the present application.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a radio wave absorbing
composition and a radio wave absorber.
2. Description of the Related Art
[0003] A radio wave absorber containing a magnetic powder as the
radio wave absorbing material is known. In addition, examples of
the radio wave absorber containing a magnetic powder include a
radio wave absorber in which a magnetic powder is mixed with a
binder (see JP2002-280207A, JP2010-260766A, and JP2012-9797A).
SUMMARY OF THE INVENTION
[0004] In recent years, as an electronic device that uses radio
waves, a radar for recognizing an object by transmitting and
receiving radio waves has attracted attention. For example, an
on-vehicle radar transmits radio waves and receives the radio waves
reflected by an object (such as a pedestrian, a vehicle, or the
like), whereby it can recognize the presence of the object, the
distance to the object, or the like. In order to prevent collision
with an object, as necessary, an automatic driving control system
of an automobile can be automatically brake and stop the automobile
or can be automatically control the speed to keep the distance to
the object based on the results obtained by the radar being
recognizing the object.
[0005] In order to improve the reliability of the system that
carries out various controls based on the results obtained by the
radar being recognizing the object as described above, it is
desired to improve the performance of the radar. For this reason,
in recent years, it has begun to be examined to install a radio
wave absorber on the front side (an incident side of the radio wave
incident from the outside) of the radio wave transmitting and
receiving unit of the radar to improve the recognition accuracy.
The radio wave absorber is required to have excellent radio wave
absorption performance in order to improve the recognition
accuracy. Further, it is desirable that the radio wave absorber has
excellent weather fastness from the viewpoint of suppressing the
deterioration of an article in which the radio wave absorber is
incorporated.
[0006] Further, a radio wave absorber having an excellent vibration
damping property is desirable since it can also function as a
vibration damping material in an article in which the radio wave
absorber is incorporated.
[0007] In consideration of the above, one aspect of the present
invention is to provide a radio wave absorber excellent in radio
wave absorption performance, weather fastness, and vibration
damping property.
[0008] As a result of diligent examinations for achieving the above
object, the inventors of the present invention have newly found
that in a case where a powder of a substitution-type hexagonal
ferrite subjected to surface treatment with a silicon-based
compound and an olefin-based resin are used in combination as a
combination of a magnetic powder and a binder, it is possible to
obtain a radio wave absorber excellent in radio wave absorption
performance, weather fastness, and vibration damping property.
[0009] That is, one aspect of the present invention relates to;
[0010] a radio wave absorbing composition comprising a magnetic
powder and a binder,
[0011] in which the magnetic powder is a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent,
[0012] the surface treatment agent is a silicon-based compound,
and
[0013] the binder is an olefin-based resin.
[0014] In addition, one aspect of the present invention relates
to;
[0015] a radio wave absorber comprising a magnetic powder and a
binder,
[0016] in which the magnetic powder is a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent,
[0017] the surface treatment agent is a silicon-based compound,
and
[0018] the binder is an olefin-based resin.
[0019] In one form, the radio wave absorber can be a molded product
formed by molding the radio wave absorbing composition.
[0020] In one form, the substitution-type hexagonal ferrite can
have a constitution represented by General Formula 1.
AFe.sub.(12-x)Al.sub.xO.sub.19 General Formula 1:
[0021] In General Formula 1, A represents one or more kinds of
atoms selected from the group consisting of Sr, Ba, Ca, and Pb, and
x satisfies 1.50.ltoreq.x.ltoreq.8.00.
[0022] In one form, the substitution-type hexagonal ferrite can be
a substitution-type hexagonal strontium ferrite.
[0023] In one form, the surface treatment agent can be a
silicon-based compound represented by General Formula 2.
(X-L).sub.m-Si--Z.sub.4-m General Formula 2:
[0024] In General Formula 2;
[0025] X is a hydrogen atom, an alkyl group, an alkenyl group, an
aryl group, an alicyclic group, a heterocyclic group, a hydroxy
group, an acrylamide group, a sulfanyl group, an isocyanate group,
a thiocyanate group, a ureido group, a cyano group, an acid
anhydride group, and an azide group, a carboxy group, an acyl
group, a thiocarbamoyl group, a phosphate group, a phosphanyl
group, a sulfonic acid group, or a sulfamoyl group,
[0026] L represents one divalent group or one bond, selected from
the group consisting of a single bond, an alkylene group, an
alkenylene group, an alkynylene group, an arylene group, --O--,
--S--, --NR.sup.a--, an ester bond, a thioester bond, an amide
bond, a thioamide bond, and a sulfonyl group, or a divalent group
or a bond, obtained by combining two or more of these,
[0027] R.sup.a represents a hydrogen atom or a substituent,
[0028] Z represents a hydroxy group, an alkoxy group, or an alkyl
group, and
[0029] m is an integer in a range of 1 to 3.
[0030] In one form, in General Formula 2, m can be 1, and X can
represent an alkenyl group or a heterocyclic group, or m can be 2
or 3, and a plurality of X's included in General Formula 2 can each
independently represent an alkenyl group or a heterocyclic
group.
[0031] In one form, in General Formula 2, m can be 1, and X can
represent an acyl group, an acrylamide group, or a heterocyclic
group, or m can be 2 or 3, and a plurality of X's included in
General Formula 2 can each independently represent an acyl group,
an acrylamide group, or a heterocyclic group, where the acyl group
can be a (meth)acryloyl group, and the heterocyclic group can be an
epoxy group.
[0032] In one form, in General Formula 2, X can represent an epoxy
group.
[0033] In one form, in General Formula 2, L can include an alkylene
group having 4 to 12 carbon atoms.
[0034] In one form, the olefin-based resin can be one or more
resins selected from the group consisting of polyethylene,
polypropylene, polymethylpentene, an ethylene-vinyl acetate resin,
a cycloolefin resin, and an olefin-based resin containing a maleic
acid anhydride unit.
[0035] In one form, the olefin-based resin can be one or more
resins selected from the group consisting of polymethylpentene, a
cycloolefin resin, and an olefin-based resin containing a maleic
acid anhydride unit.
[0036] According to one aspect of the present invention, it is
possible to provide a radio wave absorber excellent in radio wave
absorption performance, weather fastness, and vibration damping
property, and a radio wave absorbing composition that can be used
for manufacturing the radio wave absorber.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] [Radio Wave Absorbing Composition and Radio Wave
Absorber]
[0038] One embodiment of the present invention relates to a radio
wave absorbing composition containing a magnetic powder and a
binder. In the radio wave absorbing composition, the magnetic
powder is a powder of a substitution-type hexagonal ferrite
subjected to surface treatment with a surface treatment agent, the
surface treatment agent is a silicon-based compound, and the binder
is an olefin-based resin.
[0039] In addition, one embodiment of the present invention relates
to a radio wave absorber containing a magnetic powder and a binder.
In the radio wave absorber, the magnetic powder is a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent, the surface treatment agent is a
silicon-based compound, and the binder is an olefin-based
resin.
[0040] In the present invention and the present specification, the
"radio wave" shall refer to an electromagnetic wave having a
frequency of 3 terahertz (THz) or less. The radio wave absorber and
the composition that is used in the manufacture of the radio wave
absorber have radio wave absorbability. The radio wave
absorbability can be evaluated, for example, by the transmission
attenuation amount and/or the reflection attenuation amount. It can
be said that the higher the value of the transmission attenuation
amount, the higher the value of the reflection attenuation amount,
or the higher the value of the transmission attenuation amount and
the value of the reflection attenuation amount, the more excellent
the radio wave absorbability.
[0041] In the present invention and the present specification, the
"powder" means an aggregation of a plurality of particles. The
"aggregation" is not limited to an aspect in which particles that
constitute an aggregation are in direct contact with each other,
and also includes an aspect in which a binder or the like is
interposed between the particles.
[0042] Hereinafter, the radio wave absorbing composition and the
radio wave absorber will be described in more detail.
[0043] <Magnetic Powder>
[0044] The radio wave absorbing composition and the radio wave
absorber include, as a magnetic powder, a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent. The powder of the substitution-type
hexagonal ferrite subjected to surface treatment with a surface
treatment agent can also be said to be a powder of the
substitution-type hexagonal ferrite coated with a surface treatment
agent. In the powder of the substitution-type hexagonal ferrite
subjected to surface treatment with a surface treatment agent, at
least a part of the surface of at least a part of particles that
constitute the powder is coated with a surface treatment agent. The
fact that a radio wave absorber contains a magnetic powder
subjected to surface treatment with a surface treatment agent can
be confirmed, for example, by analyzing a section sample cut out
from the radio wave absorber by a known method. Alternatively, it
can be confirmed by collecting a magnetic powder from a radio wave
absorber or a radio wave absorbing composition by a known method
and analyzing the collected magnetic powder by a known method such
as mass spectrometry or gas chromatography.
[0045] (Powder of Substitution-Type Hexagonal Ferrite)
[0046] The above magnetic powder is a powder of a substitution-type
hexagonal ferrite subjected to surface treatment with a surface
treatment agent. In the present invention and the present
specification, the "powder of a hexagonal ferrite" shall refer to a
magnetic powder in which a hexagonal ferrite-type crystal structure
is detected as the main phase by X-ray diffraction analysis. The
main phase refers to a structure to which the highest intensity
diffraction peak attributes in the X-ray diffraction spectrum
obtained by X-ray diffraction analysis. For example, in a case
where the highest intensity diffraction peak in the X-ray
diffraction spectrum obtained by X-ray diffraction analysis
attributes to the hexagonal ferrite-type crystal structure, it
shall be determined that the hexagonal ferrite-type crystal
structure is detected as the main phase. In a case where only a
single structure is detected by X-ray diffraction analysis, this
detected structure is used as the main phase. The hexagonal
ferrite-type crystal structure contains at least an iron atom, a
divalent metal atom, and an oxygen atom as constituent atoms. In
the unsubstitution-type hexagonal ferrite, the atoms that
constitute the crystal structure of the hexagonal ferrite are only
the iron atom, the divalent metal atom, and the oxygen atom. On the
other hand, the substitution-type hexagonal ferrite contains one or
more kinds of other atoms together with the iron atom, the divalent
metal atom, and the oxygen atom, as atoms that constitute the
crystal structure of the hexagonal ferrite. These one or more kinds
of other atoms are generally atoms that are substituted for a part
of iron in the crystal structure of hexagonal ferrite. The divalent
metal atom is a metal atom that is capable of being a divalent
cation, as an ion, and examples thereof include an alkaline earth
metal atom such as a strontium atom, a barium atom, or a calcium
atom, and a lead atom. In the present invention and the present
specification, the "hexagonal strontium ferrite powder" means one
in which the main divalent metal atom contained in the crystal
structure of the hexagonal ferrite is a strontium atom. The main
divalent metal atom shall refer to a divalent metal atom that
occupies the largest amount among the divalent metal atoms
contained in the crystal structure of the hexagonal ferrite based
on the % by atom. However, rare earth atoms shall not be included
in the above divalent metal atoms. The "rare earth atom" in the
present invention and the present specification is selected from
the group consisting of a scandium atom (Sc), a yttrium atom (Y),
and a lanthanoid atom. The lanthanoid atom is selected from the
group consisting of a lanthanum atom (La), a cerium atom (Ce), a
praseodymium atom (Pr), a neodymium atom (Nd), a promethium atom
(Pm), a samarium atom (Sm), a europium atom (Eu), a gadolinium atom
(Gd), a terbium atom (Tb), a dysprosium atom (Dy), a holmium atom
(Ho), an erbium atom (Er), a thulium atom (Tm), a ytterbium atom
(Yb), and a lutetium atom (Lu).
[0047] The substitution-type hexagonal ferrite contains one or more
kinds of other atoms together with the iron atom, the divalent
metal atom, and the oxygen atom, as atoms that constitute the
crystal structure of the hexagonal ferrite. Examples of such atoms
include one or more kinds of trivalent metal atoms selected from
the group consisting of Al, Ga, and combinations of a divalent
metal atom and a tetravalent metal atom, such as Mn and Ti, Co and
Ti, and Zn and Ti. The substitution-type hexagonal ferrite can be
preferably a substitution-type hexagonal strontium ferrite.
[0048] In one form, the magnetic powder can be a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent, the substitution type of which is a
magnetoplumbite type (generally referred to as an "M type"). The
magnetoplumbite-type hexagonal ferrite has a constitution
represented by a constitution formula: AFe.sub.12O.sub.19 in a case
where it does not contain an atom that is substituted for iron.
Here, A can represent at least one kind of atom selected from the
group consisting of Sr, Ba, Ca, and Pb, and also includes an aspect
in which two or more of these atoms are contained in any ratio.
[0049] Examples of the hexagonal ferrite preferable from the
viewpoint of radio wave absorption performance include a
substitution-type magnetoplumbite-type hexagonal ferrite in which a
part of iron atoms of the magnetoplumbite-type hexagonal ferrite is
substituted with an aluminum atom. Examples of one embodiment of
such hexagonal ferrite include the substitution-type hexagonal
ferrite having a constitution represented by General Formula 1.
AFe.sub.(12-x)Al.sub.xO.sub.19 General Formula 1:
[0050] In General Formula 1, A represents one or more kinds of
atoms (hereinafter, also referred to as an "A atom") selected from
the group consisting of Sr, Ba, Ca, and Pb, it may be only one kind
of atom, it may contain two or more kinds of atoms in any ratio,
and, from the viewpoint of improving the uniformity of the
constitution between particles that constitute the powder, it is
preferably only one kind of atom.
[0051] From the viewpoint of radio wave absorption performance in
the high frequency band, A in General Formula 1 is preferably one
or more kinds of atoms selected from the group consisting of Sr,
Ba, and Ca, and more preferably Sr.
[0052] In General Formula 1, x satisfies 1.50.ltoreq.x.ltoreq.8.00.
From the viewpoint of radio wave absorption performance in the high
frequency band, x is 1.50 or more, more preferably more than 1.50,
still more preferably 2.00 or more, and even still more preferably
more than 2.00. In addition, from the viewpoint of magnetic
properties, x is 8.00 or less, preferably less than 8.00, more
preferably 6.00 or less, and still more preferably less than
6.00.
[0053] Specific examples of the substitution-type hexagonal ferrite
represented by General Formula 1, the substitution type of which is
a magnetoplumbite type, include
SrFe.sub.(9.58)Al.sub.(2.42)O.sub.19,
SrFe.sub.(9.37)Al.sub.(2.63)O.sub.19,
SrFe.sub.(9.27)Al.sub.(2.73)O.sub.19,
SrFe.sub.(9.85)Al.sub.(2.15)O.sub.19,
SrFe.sub.(10.00)Al.sub.(2.00)O.sub.19,
SrFe.sub.(9.74)Al.sub.(2.26)O.sub.19,
SrFe.sub.(10.44)Al.sub.(1.56)O.sub.19,
SrFe.sub.(9.79)Al.sub.(2.21)O.sub.19,
SrFe.sub.(9.33)Al.sub.(2.67)O.sub.19,
SrFe.sub.(7.88)Al.sub.(4.12)O.sub.19,
SrFe.sub.(7.04)Al.sub.(4.96)O.sub.19,
SrFe.sub.(7.37)Al.sub.(4.63)O.sub.19,
SrFe.sub.(6.25)Al.sub.(5.75)O.sub.19,
SrFe.sub.(7.71)Al.sub.(4.29)O.sub.19,
Sr.sub.(0.80)Ba.sub.(0.10)Ca.sub.(0.10)Fe.sub.(9.83)Al.sub.(2.17)O.sub.19-
, BaFe.sub.(9.50)Al.sub.(2.50)O.sub.19,
CaFe.sub.(10.00)Al.sub.(2.00)O.sub.19, and
PbFe.sub.(9.00)Al.sub.(3.00)O.sub.19. In addition, specific
examples thereof also include the substitution-type hexagonal
strontium ferrite having a constitution shown in Table 1 described
later. The constitution of hexagonal ferrite can be checked by high
frequency inductively coupled plasma emission spectroscopy.
Specific examples of the checking method include a method described
in Examples described later. Alternatively, after exposing a
cross-section by cutting the radio wave absorber or the like, the
exposed cross-section is subjected to, for example, energy
dispersive X-ray analysis, whereby the constitution of the magnetic
powder contained in the radio wave absorber can be checked.
[0054] In one form, in the powder of the substitution-type
hexagonal ferrite, the crystal phase can be a single crystal phase,
and a plurality of crystal phases can be included. It is preferable
that the crystal phase is a single phase, and it is more preferable
that the powder of the hexagonal ferrite is a powder of a
substitution-type hexagonal ferrite, the substitution type thereof
being a magnetoplumbite type, in which the crystal phase is a
single phase.
[0055] The case where the "crystal phase is a single phase" refers
to a case where only one kind of diffraction pattern showing any
crystal structure is observed in the X-ray diffraction analysis.
The X-ray diffraction analysis can be carried out, for example, by
the method described in Examples described later. In a case where a
plurality of crystal phases are included, two or more kinds of
diffraction patterns showing any crystal structure are observed in
the X-ray diffraction analysis. Regarding the attribution of the
diffraction pattern, for example, a database of the International
Centre for Diffraction Data (ICDD, registered trade name) can be
referenced. For example, regarding the diffraction pattern of the
magnetoplumbite-type hexagonal ferrite containing Sr, "00-033-1340"
of the International Centre for Diffraction Data (ICDD) can be
referred to. However, in a case where a part of iron atoms are
substituted with a substituent atom such as an aluminum atom, the
peak position shifts from the peak position observed in a case
where the substituent atom is not included.
[0056] (Method of Manufacturing Powder of Substitution-Type
Hexagonal Ferrite)
[0057] Examples of the method of manufacturing a powder of a
substitution-type hexagonal ferrite include a solid phase method
and a liquid phase method. The solid phase method is a method of
producing a powder of a hexagonal ferrite by sintering a mixture
obtained by mixing a plurality of solid raw materials in a dry-type
manner. On the other hand, the liquid phase method includes a step
of using a solution. Hereinafter, one form of the method of
manufacturing a powder of a substitution-type hexagonal ferrite by
the liquid phase method will be described. However, the
manufacturing method described below is an example, and the method
of manufacturing the magnetic powder contained in the radio wave
absorbing composition and the radio wave absorber is not limited to
the following example.
[0058] One embodiment of the liquid phase method can include;
[0059] a step 1 of obtaining a precipitate from a solution
containing an iron atom, at least one kind of atom selected from
the group consisting of Sr, Ba, Ca, and Pb, and one or more
substituent atoms that are substituted for an iron atom, and
[0060] a step 2 of sintering the precipitate obtained in the step 1
to obtain a sintered product. Hereinafter, each of the steps will
be described in detail.
[0061] Step 1
[0062] In the step 1, a hexagonal ferrite precursor can be obtained
as a precipitate. For example, in order to obtain a powder of a
hexagonal ferrite containing an aluminum atom as a substituent atom
that is substituted for a part of iron atoms, an iron atom, an A
atom, and an aluminum atom can be mixed in a solution. In this
case, it is presumed that the precipitate obtained in the step 1 is
iron hydroxide, aluminum hydroxide, a composite hydroxide of an
iron atom, an aluminum atom, and an A atom.
[0063] The solution for obtaining the precipitate in the step 1 is
preferably a solution containing at least water and is more
preferably an aqueous solution. For example, a precipitate can be
generated by mixing an aqueous solution containing various atoms
(hereinafter, also referred to as a "raw material aqueous
solution") with an alkaline aqueous solution. In addition, the step
1 can include a step of carrying out the solid-liquid separation of
the precipitate.
[0064] The raw material aqueous solution can be, for example, an
aqueous solution containing an Fe salt, an Al salt, and a salt of
an A atom. These salts can be, for example, water-soluble inorganic
acid salts such as nitrates, sulfates, and chlorides.
[0065] Specific examples of the Fe salt include iron (III) chloride
hexahydrate [FeCl.sub.3.6H.sub.2O] and iron (III) nitrate
nonahydrate [Fe(NO.sub.3).sub.3.9H.sub.2O].
[0066] Specific examples of the Al salts include aluminum chloride
hexahydrate [AlCl.sub.3.6H.sub.2O] and aluminum nitrate nonahydrate
[Al(NO.sub.3).sub.3.9H.sub.2O].
[0067] The salt of the A atom can be one or more kinds of salts
selected from the group consisting of a Sr salt, a Ba salt, a Ca
salt, and a Pb salt.
[0068] Specific examples of the Sr salt include strontium chloride
hexahydrate [SrCl.sub.2.6H.sub.2O], strontium nitrate
[Sr(NO.sub.3).sub.2], and strontium acetate 0.5 hydrate
[Sr(CH.sub.3COO).sub.2.0.5H.sub.2O].
[0069] Specific examples of the Ba salt include barium chloride
dihydrate [BaCl.sub.2.2H.sub.2O], barium nitrate
[Ba(NO.sub.3).sub.2], and barium acetate
[(CH.sub.3COO).sub.2Ba].
[0070] Specific examples of the Ca salt include calcium chloride
dihydrate [CaCl.sub.2).2H.sub.2O], calcium nitrate tetrahydrate
[Ca(NO.sub.3).sub.2.4H.sub.2O], and calcium acetate monohydrate
[(CH.sub.3COO).sub.2Ca.H.sub.2O].
[0071] Specific examples of the Pb salt include lead (II) chloride
[PbCl.sub.2] and lead (II) nitrate [Pb(NO.sub.3).sub.2].
[0072] However, the above is an example, and other salts can be
also used. The mixing ratio between various salts for preparing the
raw material aqueous solution may be determined depending on the
desired hexagonal ferrite constitution.
[0073] Examples of the alkaline aqueous solution include a sodium
hydroxide aqueous solution and a potassium hydroxide aqueous
solution. The concentration of the alkaline aqueous solution can
be, for example, 0.1 mol/L to 10 mol/L. However, the kind and the
concentration of the alkaline aqueous solution are not limited to
the above examples as long as the precipitate can be produced.
[0074] The raw material aqueous solution and the alkaline aqueous
solution may be simply mixed. The whole amount of the raw material
aqueous solution and the whole amount of the alkaline aqueous
solution may be mixed at one time, or the raw material aqueous
solution and the alkaline aqueous solution may be gradually mixed.
Alternatively, the mixing may be carried out by mixing while
gradually adding one of the raw material aqueous solution and the
alkaline aqueous solution to the other. The method of mixing the
raw material aqueous solution with the alkaline aqueous solution is
not particularly limited, and examples thereof include a method of
mixing with stirring. A stirring unit is not particularly limited
either, and a general stirring unit can be used. The stirring time
may be set to a time during which a precipitate can be formed, and
it can be appropriately set depending on the constitution of the
raw material aqueous solution, the kind of the stirring unit to be
used.
[0075] The temperature (the solution temperature) at which the raw
material aqueous solution is mixed with the alkaline aqueous
solution is, for example, preferably 100.degree. C. or lower from
the viewpoint of preventing explosive boil, and more preferably
95.degree. C. or lower and still more preferably 15.degree. C. or
higher and 92.degree. C. or lower from the viewpoint of causing the
precipitation reaction to proceed well. As a unit for adjusting the
temperature, a general heating device, cooling device, or the like
can be used. The pH of the aqueous solution obtained by mixing the
raw material aqueous solution with the alkaline aqueous solution,
at a temperature of 25.degree. C., is, for example, preferably in a
range of 5 to 13 and more preferably in a range of 6 to 12 from the
viewpoint that a precipitate is more easily obtained. The content
of the substituent atom can be controlled by adjusting the pH.
[0076] In a case where the obtained precipitate is subjected to
solid-liquid separation after the precipitate is formed, the method
of thereof is not particularly limited, and examples thereof
include decantation, centrifugation, and filtration (suction
filtration, pressure filtration, or the like). For example, in a
case where the solid-liquid separation is carried out by
centrifugation, the conditions for centrifugation are not
particularly limited, and for example, centrifugation can be
carried out for 3 to 30 minutes at a rotation speed of 2,000
revolutions per minute (rpm) or more. Further, the centrifugation
may be carried out a plurality of times.
[0077] Step 2
[0078] The step 2 is a step of sintering the precipitate obtained
in the step 1.
[0079] In the step 2, the precursor of hexagonal ferrite can be
converted to hexagonal ferrite by sintering the precipitate
obtained in the step 1. The sintering can be carried out using a
heating device. The heating device is not particularly limited, and
a known heating device such as an electric furnace, a sintering
device produced according to a production line, or the like can be
used. The sintering can be carried out, for example, in an ambient
air atmosphere. The sintering temperature and the sintering time
may be set within a range in which the precursor of hexagonal
ferrite can be converted to hexagonal ferrite. The sintering
temperature is, for example, preferably 900.degree. C. or higher,
more preferably in a range of 900.degree. C. to 1,400.degree. C.,
and still more preferably in a range of 1,000.degree. C. to
1,200.degree. C. The sintering time is, for example, preferably in
a range of 1 hour to 10 hours and more preferably in a range of 2
hours to 6 hours. In addition, the precipitate obtained in the step
1 can be dried before sintering. The drying unit is not
particularly limited, and examples thereof include a dryer such as
an oven. The drying temperature is, for example, preferably in a
range of 50.degree. C. to 200.degree. C. and more preferably in a
range of 70.degree. C. to 150.degree. C. The drying time is, for
example, preferably in a range of 2 hours to 50 hours and more
preferably in a range of 5 hours to 30 hours. The above sintering
temperature and drying temperature can be the internal ambient
temperature of the device for sintering or drying.
[0080] The sintered product obtained in the above step 2 can be an
aggregated sintered product or a powder-shaped sintered product, in
which the precursor of hexagonal ferrite is converted to show the
crystal structure of hexagonal ferrite. Further, a step of
pulverizing the sintered product can also be carried out. The
pulverization can be carried out with a known pulverizing unit such
as a mortar and pestle or a pulverizer (a cutter mill, a ball mill,
a bead mill, a roller mill, a jet mill, a hammer mill, an attritor,
or the like). For example, in the case of pulverizing using a
medium, a particle size of the medium (a so-called medium diameter)
is, for example, preferably in a range of 0.1 mm to 5.0 mm and more
preferably in a range of 0.5 mm to 3.0 mm. The "medium diameter" in
a case of a spherical medium means an arithmetic mean of diameters
of a plurality of randomly selected media (for example, beads). In
a case of a non-spherical medium (for example, a non-spherical
bead), it means an arithmetic mean of equivalent circle diameters
of a plurality of randomly selected media, which is determined from
an observation image obtained from a transmission electron
microscope (TEM) or a scanning electron microscope (SEM). Examples
of the medium material include glass, alumina, steel, zirconia, and
ceramics. In a case of pulverizing with a cutter mill, the
pulverizing conditions can be determined depending on the amount of
the sintered product to be pulverized, the scale of the cutter mill
to be used. In one form, the rotation speed of the cutter mill can
be, for example, about 5,000 to 25,000 rpm.
[0081] (Surface Treatment Agent)
[0082] The powder of the substitution-type hexagonal ferrite is
subjected to surface treatment with a surface treatment agent.
Here, the surface treatment agent is a silicon-based compound. As a
result of diligent examinations by the inventors of the present
invention, it has been newly found that in a case where a powder of
a substitution-type hexagonal ferrite subjected to surface
treatment with a silicon-based compound and an olefin-based resin
are in combination, it is possible to improve the radio wave
absorption performance, the weather fastness, and the vibration
damping property of the radio wave absorber.
[0083] Regarding the vibration damping property, it is possible to
suppress the vibration of the article by converting the vibration
energy applied to the article into thermal energy. For example, it
can be said that the larger the value of the loss coefficient,
which is said to be one of the indicators of the vibration damping
property, the better the vibration damping property. It is presumed
that with the combination of the substitution-type hexagonal
ferrite powder subjected to surface treatment with a silicon-based
compound, as a magnetic powder, and an olefin-based resin as a
binder, it is possible to increase the compatibility and the
bonding strength between the particles that constitute the magnetic
powder and the binder, and as a result, it is possible to delay the
response to mechanical deformation at the interface between the
particles and the binder, which leads to an increase in the value
of the loss coefficient.
[0084] Further, regarding the weather fastness, the interaction
between the particles that constitute the magnetic powder and the
binder can contribute to the improvement of the weather fastness.
Regarding this interaction, it is conceived that in a case where
the compatibility and the bonding strength between the particles
that constitute the magnetic powder and the binder are high,
aqueous moisture such as rainwater and moisture in the atmosphere
does not easily permeate into the radio wave absorber. It is
conceived that this makes it possible to suppress the deterioration
of the radio wave absorber due to the permeation of moisture, which
leads to the improvement of weather fastness.
[0085] However, the above is speculation and thus does not limit
the present invention.
[0086] The powder of the substitution-type hexagonal ferrite
contained in the radio wave absorbing composition and the radio
wave absorber is subjected to surface treatment with a
silicon-based compound. In the present invention and the present
specification, the "silicon-based compound" means a compound
containing silicon. The silicon-based compound can be an organic
compound or an inorganic compound and are preferably an organic
compound from the viewpoint of further improving the thermal cycle
characteristics and the cutting workability.
[0087] At least a part of groups contained in the silicon-based
compound that can be used as the surface treatment agents described
below can be a group having reactivity. The group having reactivity
means a group that can react with another group or a bond, in which
the structure after reaction is different from that before
reaction. After the surface treatment, the reactive group of the
surface treatment agent may be present in the post-reaction form in
a state where the surface treatment agent is applied onto the
powder of the substitution-type hexagonal ferrite, and such an
aspect is also included in the present invention.
[0088] Silicon-Based Compound
[0089] Examples of the silicon-based compound suitable as the
surface treatment agent include a silicon-based compound
represented by General Formula 2.
(X-L).sub.m-Si--Z.sub.4-m General Formula 2:
[0090] In General Formula 2, X represents a hydrogen atom, an alkyl
group, an alkenyl group, an aryl group, an alicyclic group, a
heterocyclic group, a hydroxy group, an acrylamide group, a
sulfanyl group, an isocyanate group, a thiocyanate group, a ureido
group, a cyano group, an acid anhydride group, an azide group, a
carboxy group, an acyl group, a thiocarbamoyl group, a phosphate
group, a phosphanyl group, a sulfonic acid group, or a sulfamoyl
group.
[0091] L represents one divalent group or one bond, selected from
the group consisting of a single bond, an alkylene group, an
alkenylene group, an alkynylene group, an arylene group, --O--,
--S--, --NR.sup.a--, an ester bond, a thioester bond, an amide
bond, a thioamide bond, and a sulfonyl group, or a divalent group
or a bond, obtained by combining two or more of these,
[0092] R.sup.a represents a hydrogen atom or a substituent.
[0093] Z represents a hydroxy group, an alkoxy group, or an alkyl
group.
[0094] m is an integer in a range of 1 to 3.
[0095] The group represented by X as well as the group and the bond
represented by L may have a substituent or can have no substituent
(for example, can be unsubstituted). Examples of the substituent
include a hydroxy group, a sulfanyl group, a thiocyanate group, a
ureido group, an acid anhydride group, a carboxy group, an acyl
group, and a carbamoyl group. In the present invention and the
present specification, regarding a group having a substituent and a
bond, the number of carbon atoms shall refer to the number of
carbon atoms of a portion other than the substituent unless
otherwise specified. In the structure represented by "X-L-", in a
case where there is a portion that may be interpreted as a portion
that is contained in X as well as a portion that is contained in L,
such a portion shall be interpreted as a portion that is contained
in X.
[0096] In a case where m is 2 or 3, a plurality of X's included in
General Formula 2 can be the same in one form and can be different
from each other in another form. This point also identically
applies to L. In addition, the same also identically applies to Z
in a case where "4-m" is 2 or 3.
[0097] Hereinafter, General Formula 2 will be described in more
detail.
[0098] In General Formula 2, X represents a hydrogen atom, an alkyl
group, an alkenyl group, an aryl group, an alicyclic group, a
heterocyclic group, a hydroxy group, an acrylamide group, a
sulfanyl group, an isocyanate group, a thiocyanate group, a ureido
group, a cyano group, an acid anhydride group, an azide group, a
carboxy group, an acyl group, a thiocarbamoyl group, a phosphate
group, a phosphanyl group, a sulfonic acid group, or a sulfamoyl
group.
[0099] The numbers of carbon atoms of the alkyl group, the alkenyl
group, and the aryl group, that can be adopted as X, are each
independently preferably in a range of 1 to 30, more preferably in
a range of 1 to 25, still more preferably in a range of 1 to 20,
and even still more preferably in a range of 1 to 15. Unless
otherwise specified in the present invention and the present
specification, the "alkyl group" shall not include a cycloalkyl
group. The alkyl group includes a linear alkyl group and a branched
alkyl group.
[0100] The alicyclic group that can be adopted as X may be any of a
cycloalkyl group, a cycloalkenyl group, and a cycloalkynyl group.
The number of carbon atoms of the cycloalkyl group is preferably in
a range of 3 to 20, more preferably in a range of 4 to 15, and
still more preferably in a range of 5 to 10. The numbers of carbon
atoms of the cycloalkenyl group and the cycloalkynyl group are each
independently preferably in a range of 6 to 20, more preferably in
a range of 6 to 15, still more preferably in a range of 6 to 10,
and even still more preferably 6.
[0101] The heterocyclic ring constituting a heterocyclic group that
can be adopted as X may be a saturated or unsaturated aliphatic
heterocyclic ring or aromatic heterocyclic ring, and may be a
monocyclic ring or a fused ring. It may also be a bridged ring.
Examples of the heteroatom contained in the heterocyclic ring
include an oxygen atom, a nitrogen atom, and a sulfur atom. The
number of heteroatoms contained in one heterocyclic ring is not
particularly limited, and the heterocyclic ring has, for example,
preferably 1 to 3 carbon atoms and more preferably 1 or 2 carbon
atoms. The number of carbon atoms in the heterocyclic ring is
preferably in a range of 2 to 10, and more preferably 4 or 5. The
heterocyclic ring is preferably a 3-membered to 7-membered ring,
more preferably a 3-membered to 6-membered ring, and still more
preferably a 3-membered to 5-membered ring. Specific examples of
the heterocyclic ring include an epoxy ring, a 3,4-epoxycyclohexane
ring, a furan ring, and a thiophene ring. In one form, the
heterocyclic group represented by X can be an epoxy group. In the
present invention and the present specification, the "epoxy group"
shall include an aspect in which the heterocyclic ring contained in
the epoxy group is an epoxy ring (a 3-membered ring) and an aspect
which includes a cyclic group having a structure in which an epoxy
ring and a saturated hydrocarbon ring are fused. Examples of such a
cyclic group include a 3,4-epoxycyclohexane ring.
[0102] The acid anhydride group that can be adopted as X is
preferably a monovalent group having a structure of a carboxylic
acid anhydride, and examples thereof include a maleic acid
anhydride group such as 3,4-dihydro-2,5-furandionyl, a succinic
acid anhydride group, a glutaric acid anhydride group, an adipic
acid anhydride group, and a citraconic acid anhydride group.
[0103] The number of carbon atoms of the acyl group that can be
adopted as X is preferably in a range of 1 to 40, more preferably
in a range of 1 to 30, still more preferably in a range of 1 to 20,
and even still more preferably in a range of 2 to 15. In the
present invention and the present specification, the "acyl group"
includes a formyl group, a carbamoyl group, an alkylcarbonyl group,
an alkenylcarbonyl group, and an arylcarbonyl group. Examples of
the alkenylcarbonyl group preferably includes a (meth)acryloyl
group. In the present invention and the present specification, the
"(meth)acryloyl group" includes an acryloyl group and a
methacryloyl group.
[0104] The alkylene group that can be adopted as L may be any one
of a linear alkylene group or a branched alkylene group. The number
of carbon atoms of the alkylene group that can be adopted as X is
preferably in a range of 1 to 30, more preferably in a range of 2
to 25, still more preferably in a range of 3 to 20, and even still
more preferably in a range of 4 to 12. Specific examples of the
alkylene group include a methylene group, an ethylene group, an
isopropylene group, a butylene group, a pentylene group, a
cyclohexylene group, a heptylene group, an octylene group, a
nonylene group, a decylene group, and an undecylene group.
[0105] The alkenylene group that can be adopted as L may be any one
of a linear alkenylene group or a branched alkenylene group. The
number of carbon atoms of the alkenylene group that can be adopted
as X is preferably in a range of 2 to 20, more preferably in a
range of 2 to 15, still more preferably in a range of 2 to 10, and
even still more preferably in a range of 2 to 6. Specific examples
of the alkenylene group include an ethenylene group and a
propenylene group.
[0106] The alkynylene group that can be adopted as L may be any one
of a linear alkynylene group or a branched alkynylene group. The
number of carbon atoms of the alkynylene group that can be adopted
as X is preferably in a range of 2 to 20, more preferably in a
range of 2 to 15, still more preferably in a range of 2 to 10, and
even still more preferably in a range of 2 to 6. Specific examples
of the alkynylene group include an ethynylene group and a
propynylene group.
[0107] The number of carbon atoms of the arylene group that can be
adopted as L is preferably in a range of 6 to 20, more preferably
in a range of 6 to 15, still more preferably in a range of 6 to 12,
and even still more preferably in a range of 6 to 10. Specific
examples of the arylene group include a phenylene group and a
naphthylene group.
[0108] Examples of the substituent as R.sup.a of --NR.sup.a-- that
can be adopted as L include an alkyl group (preferably having 1 to
12 carbon atoms and more preferably 1 to 8 carbon atoms) an alkenyl
group (preferably having 2 to 12 carbon atoms and more preferably
having 2 to 8 carbon atoms) an alkynyl group (preferably having 2
to 12 carbon atoms and more preferably having 2 to 8 carbon atoms),
an aryl group (preferably having 6 to 20 carbon atoms and more
preferably having 6 to 10 carbon atoms), and a heterocyclic group.
Examples of the heterocyclic ring constituting a heterocyclic group
that can be adopted as R.sup.a include the heterocyclic ring
described above as the heterocyclic ring constituting a
heterocyclic group that can be adopted as X, and the preferred
heterocyclic group is also as described for the heterocyclic group
that can be adopted as X. Examples of --NR.sup.a-- include
--NH--.
[0109] In a case where L represents a divalent group (hereinafter,
also described as a "combined group that can be adopted as L")
obtained by combining two or more selected from the group
consisting of a single bond, an alkylene group, an alkenylene
group, an alkynylene group, an arylene group, --O--, --S--,
--NR.sup.a--, an ester bond, a thioester bond, an amide bond, a
thioamide bond, and a sulfonyl group, the numbers of the
above-described groups and bonds, which constitute the combined
group that can be adopted as L, are preferably in a range of 2 to
8, more preferably in a range of 2 to 6, and still more preferably
in a range of 2 to 4.
[0110] The molecular weight of the combined group that can be
adopted as L is preferably in a range of 20 to 1,000, more
preferably in a range of 30 to 500, and still more preferably in a
range of 40 to 200.
[0111] Examples of the combined group that can be adopted as L
include a urea bond, a thiourea bond, a carbamate group, a
sulfonamide bond, an arylene group-alkylene group, an --O-alkylene
group, an amide bond-alkylene group, an --S-alkylene group, an
alkylene group-O-amide bond-alkylene group, an alkylene group-amide
bond-alkylene group, an alkenylene group-amide bond-alkylene group,
an alkylene group-ester bond-alkylene group, an arylene group-ester
bond-alkylene group, -(alkylene group-O)--, an alkylene
group-O-(alkylene group-O)-alkylene group (here, any "(alkylene
group-O)" is a repeating unit), an arylene group-sulfonyl
group-O-alkylene group, and an ester bond-alkylene group.
[0112] Regarding the alkyl group constituting an alkoxy group that
can be adopted as Z, the "alkyl group" includes a cycloalkyl group
as well. The alkyl group constituting an alkoxy group that can be
adopted as Z may be any one of a linear alkyl group, a branched
alkyl group, or a cycloalkyl group, and it may have a combination
of these forms. The alkyl group that can be taken as Z is
preferably a linear alkyl group.
[0113] The number of carbon atoms of the alkyl group constituting
an alkoxy group that can be adopted as Z, is preferably in a range
of 1 to 15, more preferably in a range of 1 to 10, still more
preferably in a range of 1 to 5, and even still more preferably 1
or 2. Specific examples of the alkyl group that constitutes an
alkoxy group include a methyl group, an ethyl group, a propyl
group, a t-butyl group, a pentyl group, and a cyclohexyl group.
[0114] Examples of the alkyl group that can be adopted as Z include
an alkyl group constituting an alkoxy group that can be adopted as
Z, and the preferred alkyl group is also as described for the alkyl
group constituting an alkoxy group that can be adopted as Z.
[0115] In General Formula 2, X or L and at least one of Z's may be
linked to each other to form a ring. The number of
ring-constituting atoms in this ring is preferably in a range of 3
to 10, more preferably in a range of 4 to 8, and still more
preferably 5 or 6.
[0116] In General Formula 2, X preferably represents a hydrogen
atom, an alicyclic group, a heterocyclic group, an acrylamide
group, a hydroxy group, a sulfanyl group, a thiocyanate group, an
acid anhydride group, a carboxy group, an acyl group, or a sulfonic
acid group. In addition, L preferably represents one divalent group
or one bond, selected from the group consisting of an alkylene
group, an alkenylene group, an alkynylene group, an arylene group,
--O--, --S--, --NR.sup.a--, an ester bond, a thioester bond, an
amide bond, and a sulfonyl group, or a divalent group or a bond,
obtained by combining two or more of these.
[0117] In one form, in General Formula 2, m can be 1, and X can
represent an alkenyl group or a heterocyclic group. In another
form, m can be 2 or 3, and a plurality of X's included in General
Formula 2 can each independently represent an alkenyl group or a
heterocyclic group.
[0118] In addition, in one form, in General Formula 2, m can be 1
and X can represent a (meth)acryloyl group, an acrylamide group, or
an epoxy group. In another form, m can be 2 or 3, and a plurality
of X's included in General Formula 2 can each independently
represent a (meth)acryloyl group, an acrylamide group, or an epoxy
group.
[0119] In one form, in General Formula 2, X preferably represents a
(meth)acryloyl group, an acrylamide group, or an epoxy group. In
addition, L more preferably represents one divalent group or one
bond, selected from the group consisting of an alkylene group, an
alkenylene group, --O--, --NR.sup.a--, an ester bond, and an amide
bond, or a divalent group or a bond, obtained by combining two or
more of these.
[0120] In one form, in General Formula 2, it is preferable that at
least two of Z's are selected from the group consisting of an
alkoxy group and a hydroxy group, and it is more preferable that
all Z's are selected from the group consisting of an alkoxy group
and a hydroxy group.
[0121] In addition, from the viewpoint of further improving the
cutting workability, a silicon-based compound containing an epoxy
group is preferable, an epoxysilane is more preferable, and an
epoxysilane having a large number of carbon atoms is still more
preferable. This is presumed to be because the flexibility at the
interface between the surface of the magnetic powder particles and
the resin described later is increased. From this point, in General
Formula 2, it is preferable that X represents an epoxy group, and
it is more preferable that X represents an epoxy group and L
includes an alkylene group having 4 to 12 carbon atoms.
[0122] Specific examples of the silicon-based compound that can be
used as a surface treatment agent include various compounds that
are used in Examples described later. In addition, specific
examples of the silicon-based compound that can be used as a
surface treatment agent include the following various compounds.
However, the present invention is not limited to these specific
examples. [0123] Methyltriacetoxysilane, [0124]
ethyltriethoxysilane, [0125] methyltriethoxysilane, [0126]
methyltrimethoxysilane, [0127] n-propyltrimethoxysilane, [0128]
isopropyltrimethoxysilane, [0129] n-hexyltrimethoxysilane, [0130]
n-dodecyltriethoxysilane, [0131] n-octyltriethoxysilane, [0132]
n-octadecyltriethoxysilane, [0133] pentyltriethoxysilane, [0134]
diacetoxydimethylsilane, [0135] diethoxydimethylsilane, [0136]
dimethoxydimethylsilane, [0137] dimethoxydiphenylsilane, [0138]
dimethoxymethylphenylsilane, [0139] vinyldiethoxymethylsilane,
[0140] vinyltris(2-methoxyethoxy)silane, [0141]
p-styryltriethoxysilane, [0142] naphthylltrimethoxysilane, [0143]
anthryltrimethoxysilane, [0144] benzyltrimethoxysilane, [0145]
3-glycidyloxypropyl(dimethoxy)methylsilane, [0146]
diethoxy(3-glycidyloxypropyl)methylsilane, [0147]
3-(2-aminoethylamino)propyldimethoxymethylsilane, [0148]
3-(2-aminoethylamino)propyltriethoxysilane, [0149]
3-(2-aminoethylamino)propyltrimethoxysilane, [0150]
3-aminopropyldiethoxymethylsilane, [0151]
3-aminopropyltriethoxysilane, [0152] 3-aminopropyltrimethoxysilane,
[0153] (3-mercaptopropyl)triiethoxysilane, [0154]
(3-mercaptopropyl)trimethoxysilane, [0155] 3-isocyanate
propyltriethoxysilane, [0156] 3-acryloxypropyltrimethoxysilane,
[0157] triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane, [0158]
2-cyanoethyltriethoxysilane, [0159] thienyltrimethoxysilane, [0160]
pyridyltrimethoxysilane, and [0161] furyltriethoxysilane.
[0162] In the present invention and the present specification, the
silicon-based compound represented by General Formula 2 also
includes a form of a salt of the compound represented by General
Formula 2. Examples of the form of the salt thereof include an
alkali metal salt such as a sodium salt or a potassium salt, an
alkaline earth metal salt such as a magnesium salt, and an ammonium
salt.
[0163] In addition, in one form, examples of the silicon-based
compound include a silicone-based compound. Examples of the
silicone-based compound include a polydimethylsiloxane, a
polyalkylene oxide-modified silicone, a hydrogenated polysiloxane
such as a hydrogen-terminated polydimethylsiloxane, a
methylhydrosiloxane-dimethylsiloxane copolymer, and a
polymethylhydrosiloxane. The molecular weight of the silicone-based
compound is not particularly limited. In one form, the molecular
weight of the silicone-based compound is preferably about 1 to
300,000 as a weight-average molecular weight. In one form, the
liquid silicone-based compound preferably has a viscosity of 100 to
60,000 centistokes (cSt) (measurement temperature: 25.degree. C.)
from the viewpoint of surface treatment efficiency. In one form,
the polyalkylene oxide-modified silicone preferably has an alkylene
oxide content in a range of 10% to 90% by mass and more preferably
in a range of 20% to 80% by mass. In one form, the content of the
methylhydrosiloxane unit in the case of the hydrogenated
polysiloxane is preferably in a range of 0.1% to 100% by mole and
more preferably in a range of 2% to 50% by mole.
[0164] The silicon-based compound described above may be used
alone, or two or more thereof can be used in combination at any
ratio. In a case where a powder of a substitution-type hexagonal
ferrite is subjected to surface treatment by subjecting the
silicon-based compound (the surface treatment agent) to dry-type
mixing or wet-type mixing with the powder of the substitution-type
hexagonal ferrite, it is possible to coat at least a part of the
surface of at least a part of particles that constitute the powder.
As the surface treatment method, a known technique for surface
treatment using a surface treatment agent can be adopted. The using
amount of the surface treatment agent in the surface treatment is
preferably in a range of 0.1 to 100 parts by mass and more
preferably in a range of 0.5 to 20 parts by mass with respect to
100 parts by mass of the powder of the substitution-type hexagonal
ferrite.
[0165] The radio wave absorbing composition and the radio wave
absorber include, as a magnetic powder, a powder of a
substitution-type hexagonal ferrite subjected to surface treatment
with the surface treatment agent described above. In the radio wave
absorbing composition and the radio wave absorber, the filling rate
of the powder of the substitution-type hexagonal ferrite subjected
to surface treatment with the surface treatment agent is not
particularly limited. For example, the filling rate can be 35% by
volume or less and can be also in a range of 15% to 35% by volume
in terms of the volume filling rate. In addition, in one form, the
volume filling rate can be 35% by volume or more. In this case, the
volume filling rate can be, for example, in a range of 35% to 60%
by volume and is preferably in a range of 35% to 50% by volume.
Regarding the radio wave absorber, the volume filling rate
described above means a volume-based content with respect to 100%
by volume of the total volume of the radio wave absorber. Regarding
the radio wave absorbing composition, the volume filling rate means
a volume-based content of solid contents (that is, components
excluding the solvent) with respect to 100% by volume of the total
volume.
[0166] In addition, from the viewpoint of radio wave absorption
performance, in the radio wave absorbing composition and the radio
wave absorber, the powder of the substitution-type hexagonal
ferrite subjected to surface treatment with a surface treatment
agent is preferably contained in an amount of 10% by mass or more,
more preferably 30% by mass or more, and still more preferably 50%
by mass or more, with respect to the total mass (100% by mass) of
this powder and the resin described later. On the other hand, from
the viewpoint of weather fastness, in the radio wave absorbing
composition and the radio wave absorber, the powder of the
substitution-type hexagonal ferrite subjected to surface treatment
with a surface treatment agent is preferably contained in an amount
of 90% by mass or less, more preferably 80% by mass or less, and
still more preferably 75% by mass or less, with respect to the
total mass (100% by mass) of this powder and the resin described
later.
[0167] <Binder>
[0168] The radio wave absorbing composition and the radio wave
absorber include the magnetic powder and the binder. The binder is
a resin, and the radio wave absorbing composition and the radio
wave absorber contains an olefin-based resin as the binder.
Combining the olefin-based resin with the powder of the
substitution-type hexagonal ferrite subjected to surface treatment
with a silicon-based compound can contribute to the improvement of
the radio wave absorption performance, the weather fastness, and
the vibration damping property of the radio wave absorber.
[0169] The olefin-based resin is a polymer having a polymerizable
component containing at least olefin (a double bond-containing
compound). In the present invention and the present specification,
the "polymer" and the "resin" can be a homopolymer or a copolymer.
Examples of the olefin include .alpha.-olefins such as ethylene,
propylene, 1-butene, and 4-methyl-1-pentene. Examples of the
.alpha.-olefin polymer, that is, the poly-.alpha.-olefin, include
polyethylene, polypropylene, polybutene, polymethylpentene. The
polyethylene can be various kinds of polyethylene such as
low-density polyethylene, medium-density polyethylene, high-density
polyethylene, linear low-density polyethylene, linear
ultra-low-density polyethylene, and metallocene-catalyzed linear
short-chain branched polyethylene. Examples of the copolymer
include a random copolymer and a block copolymer of a
poly-.alpha.-olefin, a random copolymer of an .alpha.-olefin and an
unsaturated fatty acid, and a graft copolymer of an .alpha.-olefin
and an unsaturated fatty acid or anhydride thereof.
[0170] Examples of the random copolymer of an .alpha.-olefin and an
unsaturated fatty acid include an ethylene-vinyl acetate resin, an
ethylene-ethyl acrylate resin, an ethylene-acrylic acid resin, an
ethylene-methacrylic acid resin, and an acid-modified olefin-based
resin obtained by modifying polyethylene or polypropylene with an
unsaturated carboxylic acid such as acrylic acid, methacrylic acid,
maleic acid anhydride, fumaric acid, or itaconic acid.
[0171] Examples of the unsaturated fatty acid in the graft
copolymer of an .alpha.-olefin and an unsaturated fatty acid or
anhydride thereof include monobasic unsaturated fatty acids such as
acrylic acid and methacrylic acid, and anhydrides thereof; and
dibasic unsaturated fatty acids such as maleic acid, fumaric acid,
and itaconic acid, and anhydrides thereof. Examples of the graft
copolymer of an .alpha.-olefin and an unsaturated fatty acid or
anhydride thereof include a maleic acid-grafted ethylene-vinyl
acetate resin, a maleic acid-grafted ethylene-.alpha.-olefin resin,
and an ethylene-methacrylate-glycidylacrylate ternary polymer.
[0172] In one form, the olefin-based resin can be a polymer having
a polymerizable component containing at least cycloolefin, that is,
a cycloolefin resin.
[0173] Examples of the cycloolefin include bicyclic cycloolefins
such as norbornene, norbornadiene, methylnorbornene,
dimethylnorbornene, ethylnorbornene, chlorinated norbornene,
chloromethylnorbornene, trimethylsilylnorbornene, phenylnorbornene,
cyanonorbornene, dicyanonorbornene, methoxycarbonylnorbornene,
pyridylnorbornene, a nadic acid anhydride, and a nadic acid imide;
tricyclic cycloolefins such as dicyclopentadiene,
dihydrodicyclopentadiene, alkyl-substituted products thereof,
alkenyl-substituted products thereof, alkylidene-substituted
products thereof, and aryl-substituted products thereof;
tetracyclic cycloolefins such as dimethanohexahydronaphthalene,
dimethanooctahydronaphthalene, alkyl-substituted products thereof,
alkenyl-substituted products thereof, alkylidene-substituted
products thereof, and aryl-substituted products thereof;
pentacyclic cycloolefins such as tricyclopentadiene; and hexacyclic
cycloolefins such as hexacycloheptadecene. In addition, examples
thereof include dinorbornene, a compound in which two norbornene
rings are bonded by a hydrocarbon chain or an ester group, and
alkyl-substituted products thereof, aryl-substituted products
thereof, or the like, which is a compound containing a norbornene
ring.
[0174] Examples of the cycloolefin resin include a polymer of
cycloolefin, and a hydrogen-added product thereof; a copolymer of
cycloolefin and another olefin such as ethylene, and a
hydrogen-added product thereof; and various cycloolefin resins
(cycloolefin co-polymer; COC) such as a copolymer of cycloolefin
and another polymerizable compound. Examples of the cycloolefin
resin which is a copolymer of cycloolefin and another polymerizable
compound include an ethylene-norbornene resin and a
dicyclopentadiene resin.
[0175] In one form, the olefin-based resin can be one or more
resins selected from the group consisting of polyethylene,
polypropylene, polymethylpentene, an ethylene-vinyl acetate resin,
a cycloolefin resin, and an olefin-based resin containing a maleic
acid anhydride unit. The "olefin-based resin containing a maleic
acid anhydride unit" is a polymer having a polymerizable component
containing olefin and a maleic acid anhydride. Specific examples
thereof include an ethylene-vinyl acetate-maleic acid anhydride
resin, a maleic acid anhydride graft-polyethylene resin, an
ethylene-acrylic acid ester-maleic acid anhydride resin. Here, the
notation "-" regarding the resin is used to represent a copolymer.
For example, the "ethylene-vinyl acetate resin" is a copolymer of
polymerizable components containing ethylene and vinyl acetate. In
addition, for example, the "ethylene-vinyl acetate-maleic acid
anhydride resin" is a copolymer of polymerizable components
containing ethylene, vinyl acetate, and a maleic acid anhydride,
and it is also an ethylene-vinyl acetate resin and is an
olefin-based resin containing a maleic acid anhydride unit" as
well.
[0176] In the polymer component, the "molecular weight" in the
present invention and the present specification means the
weight-average molecular weight. The molecular weight of the
olefin-based resin is not particularly limited. In one form, the
lower limit of the weight-average molecular weight (Mw) is
preferably 10,000 or more, more preferably 20,000 or more, and
still more preferably 50,000 or more, from the viewpoint that a
vibration damping property and weather fastness tend to be easily
exhibited. In addition, in one form, the upper limit thereof is
preferably 1,000,000 or less and more preferably 500,000 or less
from the same viewpoint as described above. The "weight-average
molecular weight" in the present invention and the present
specification means a relative molecular weight with respect to the
molecular weight of the standard polystyrene, which is analyzed by
gel permeation chromatography using o-dichlorobenzene as the mobile
phase.
[0177] In addition, in one form, the olefin-based resin can be one
or more resins selected from the group consisting of
polymethylpentene, a cycloolefin resin, and an olefin-based resin
containing a maleic acid anhydride unit.
[0178] Specific examples of the commercially available product of
the olefin-based resin include high-density polyethylene (HDPE;
HI-ZEX 232J manufactured by Prime Polymer Co., Ltd.), polypropylene
(PP; NOVATEC MA3 manufactured by Japan Polypropylene Corporation),
an ethylene-vinyl acetate resin (EVA; Ultrathene 537 manufactured
by Tosoh Corporation), an ethylene-vinyl acetate-maleic acid
anhydride resin (OREVAC T 9314 manufactured by Arkema S.A.), a
maleic acid anhydride graft-polyethylene resin (OREVAC G OE808
manufactured by Arkema S.A.), an ethylene-acrylic acid ester-maleic
acid anhydride resin (BONDINE 5500 manufactured by Arkema S.A.), a
cycloolefin resin (ZEONOR 1020R manufactured by ZEON CORPORATION),
a polymethylpentene resin (TPX RT18 manufactured by Mitsui
Chemicals, Inc.), an ethylene-norbornene resin (Topas 8007S-04
manufactured by Polyplastics Co., Ltd.), a dicyclopentadiene resin
(METTON T02 manufactured by RIMTEC Corporation), a cycloolefin
resin (APEL APL8008T manufactured by Mitsui Chemicals, Inc.), and a
cycloolefin resin (ARTON D4000 manufactured by JSR
Corporation).
[0179] The radio wave absorbing composition and the radio wave
absorber may contain only one kind of the resin or may contain two
or more kinds of the resins in any ratio. The filling rate of the
olefin-based resin in the radio wave absorbing composition and the
radio wave absorber is not particularly limited; however, the
volume filling rate thereof is, for example, preferably 65% by
volume or more, more preferably 65% by volume or more and 92% by
volume or less, and still more preferably 65% by volume or more and
85% by volume or less. In a case where the radio wave absorbing
composition and the radio wave absorber contain two or more kinds
of olefin-based resins, the filling rate shall refer to the total
filling rate of two or more kinds of olefin-based resins. This
point also identically applies to the filling rates of other
components.
[0180] <Additive>
[0181] The radio wave absorbing composition and the radio wave
absorber contain the powder of the substitution-type hexagonal
ferrite subjected to surface treatment with a silicon-based
compound and the olefin-based resin, and may optionally contain one
or more additives. Examples of the additive include a dispersing
agent, a dispersing auxiliary agent, a fungicide, an antistatic
agent, and an antioxidant. One component of the additive may carry
out two or more functions. The radio wave absorbing composition and
the radio wave absorber can contain, as the additive, a
commercially available product or a product produced by a known
method at any filling rate.
[0182] <Methods of Manufacturing Radio Wave Absorbing
Composition and Radio Wave Absorber>
[0183] The methods of manufacturing the radio wave absorbing
composition and the radio wave absorber are not particularly
limited. The radio wave absorbing composition of the present
disclosure can be manufactured by a known method using the magnetic
powder, an olefin-based resin, and, as necessary, a solvent, an
additive, and the like. For example, the radio wave absorber can be
a molded product formed by molding the radio wave absorbing
composition. The radio wave absorbing composition can be prepared
as a kneaded material by kneading, while heating, a mixture of the
magnetic powder, the resin, and, as necessary, a solvent,
additives, and the like. The kneaded material can be obtained, for
example, as a pellet. The kneaded material is molded into a desired
shape by a known molding method such as extrusion molding, press
molding, injection molding, or in-mold forming, whereby a radio
wave absorber (a molded product) can be obtained. The shape of the
radio wave absorber is not particularly limited and may be any
shape such as a plate shape or a linear shape. The "plate shape"
includes a sheet shape and a film shape. The plate-shaped radio
wave absorber can also be called a radio wave absorbing plate, a
radio wave absorbing sheet, a radio wave absorbing film, or the
like. The radio wave absorber may be a radio wave absorber having a
single constitution (for example, a single-layer radio wave
absorbing plate) or a combination of two or more parts having
different constitutions (for example, a laminate). Further, the
radio wave absorber may have a planar shape, may have a
three-dimensional shape, or may be a combination of a portion
having a planar shape and a portion having a three-dimensional
shape. Examples of the planar shape include a sheet shape and a
film shape. Examples of the three-dimensional shape include a
tubular shape (a cylindrical shape, rectangular tubular shape, or
the like), a horn shape, and a box shape (for example, at least one
of the surfaces thereof is open).
[0184] For example, the thickness of the radio wave absorber is
preferably 20.0 mm or less, more preferably 10.0 mm or less, and
still more preferably 5.0 mm or less, from the viewpoint of
easiness of handling. From the viewpoint of mechanical properties,
the thickness thereof is preferably 1.0 mm or more and more
preferably 2.0 mm or more. In a case where the thickness of the
radio wave absorber is adjusted, for example, the transmission
attenuation amount described later can be controlled. In a case
where the radio wave absorber is a laminate, the thickness means
the total thickness of the radio wave absorber that constitutes the
laminate. The thickness of the radio wave absorber is a value
measured using a digital length measuring machine and,
specifically, is an arithmetic mean of the measured values measured
at nine points which are randomly selected.
[0185] The radio wave absorbing composition may contain or may not
contain a solvent. In a case where the radio wave absorbing
composition contains a solvent, the solvent is not particularly
limited, and examples thereof include water, an organic solvent,
and a mixed solvent of water and an organic solvent.
[0186] Examples of the organic solvent include alcohols such as
methanol, ethanol, n-propanol, i-propanol, and methoxypropanol,
ketones such as acetone, methyl ethyl ketone, and cyclohexanone,
tetrahydrofuran, acetonitrile, ethyl acetate, and toluene. Among
these, the solvent is preferably ketones and more preferably
cyclohexanone from the viewpoint of drying rate. In a case where
the radio wave absorbing composition contains a solvent, the
content of the solvent in the composition is not particularly
limited and may be determined depending on the method of
manufacturing a radio wave absorber.
[0187] The radio wave absorbing composition can be prepared by
mixing the above components. The mixing method is not particularly
limited, and examples thereof include a method of mixing by
stirring. As the stirring unit, a known stirring device can be
used. Examples of the stirring device include mixers such as a
paddle mixer and an impeller mixer. The stirring time may be set
depending on the kind of the stirring device, the constitution of
the radio wave absorbing composition, and the like.
[0188] Examples of one form of the method of manufacturing the
radio wave absorber include a method of molding the radio wave
absorbing composition into a desired shape by a known molding
method as exemplified above.
[0189] In addition, examples of another form of the method of
manufacturing the radio wave absorber include a method of applying
the radio wave absorbing composition onto a support and producing
the radio wave absorber as a radio wave absorbing layer. The
support that is used here may be removed before the radio wave
absorber is incorporated into an article to which the radio wave
absorbability should be imparted or may be incorporated into the
article together with the radio wave absorber without being
removed.
[0190] The support is not particularly limited, and a well known
support can be used. Examples of the support include a metal plate
(a plate of metal such as aluminum, zinc, or copper), a glass
plate, a plastic sheet [a sheet of polyester (polyethylene
terephthalate, polyethylene naphthalate, or polybutylene
terephthalate), polyethylene (linear low-density polyethylene,
low-density polyethylene, or high-density polyethylene),
polypropylene, polystyrene, polycarbonate, polyimide, polyamide,
polyamide imide, polysulfone, polyvinyl chloride,
polyacrylonitrile, polyphenylene sulfide, polyether imide,
polyether sulfone, polyvinyl acetal, or an acrylic resin], a
plastic sheet on which the metal exemplified in the metal plate
described above is laminated or vapor-deposited. The plastic sheet
is preferably biaxially stretched. The shape, structure, size, and
the like of the support can be appropriately selected.
[0191] Examples of the shape of the support include a plate shape.
The structure of the support may be a monolayer structure or a
laminated structure of two or more layers. The size of the support
can be appropriately selected depending on the size of the radio
wave absorber. The thickness of the support is generally
approximately 0.01 mm to 10 mm, for example, preferably 0.02 mm to
3 mm and more preferably 0.05 mm to 1 mm, from the viewpoint of
handleability.
[0192] The method of applying the radio wave absorbing composition
on a support is not particularly limited, and examples thereof
include methods using a die coater, a knife coater, an applicator.
The method of drying the coating film formed by applying the radio
wave absorbing composition is not particularly limited, and
examples thereof include a method using a known heating device such
as an oven. The drying temperature and the drying time are not
particularly limited. For example, the drying temperature can be in
a range of 70.degree. C. to 90.degree. C., and the drying time can
be in a range of 1 hour to 3 hours.
[0193] The radio wave absorber can be incorporated into various
articles to which radio wave absorbability is desired to be
imparted. For example, the plate-shaped radio wave absorber can be
incorporated into an article in any form as it is or by being bent
at any portion. In addition, it can be adjusted to a desired shape
by injection molding or the like to be incorporated into an
article.
[0194] A radio wave absorber having excellent radio wave absorption
performance is useful for improving the recognition accuracy of
radar. Examples of the indicator of the radio wave absorption
performance include the transmission attenuation amount. For
example, the transmission attenuation amount of the radio wave
absorber can be 6.0 dB or more. In order to improve the recognition
accuracy of the radar, it is desirable to increase the directivity
of the radar. A high transmission attenuation amount can contribute
to the improvement of the directivity of the radar. From the
viewpoint of further improving the directivity of the radar, the
transmission attenuation amount of the radio wave absorber is
preferably 8.0 dB or more, more preferably 8.5 dB or more, still
more preferably 9.0 dB or more, and even still more preferably 10.0
dB or more. The transmission attenuation amount of the radio wave
absorber can be, for example, 15.0 dB or less, 14.5 dB or less,
14.0 dB or less, 13.5 dB or less, 13.0 dB or less, 12.5 dB or less,
or 12.0 dB or less. However, from the viewpoint of improving the
directivity of the radar, it is preferable that the transmission
attenuation amount of the radio wave absorber is high. Accordingly,
the transmission attenuation amount of the radio wave absorber may
exceed the values exemplified above.
[0195] Further, the reflection attenuation amount of the radio wave
absorber can be, for example, 6.0 dB or more. In order to improve
the recognition accuracy of the radar, it is desirable to enhance
the selectivity of the radar by removing or reducing unnecessary
radio wave components with the radio wave absorber, where the
selectivity is receiving radio waves selectively from an object. A
high reflection attenuation amount can contribute to the removal or
reduction of unnecessary radio wave components. From this point,
the reflection attenuation amount of the radio wave absorber is
preferably 8.0 dB or more, more preferably 8.5 dB or more, still
more preferably 9.0 dB or more, and even still more preferably 10.0
dB or more. The reflection attenuation amount of the radio wave
absorber can be, for example, 18.0 dB or less, 17.5 dB or less,
17.0 dB or less, 16.5 dB or less, 16.0 dB or less, 15.5 dB or less,
or 15.0 dB or less. However, from the viewpoint of removing or
reducing unnecessary radio wave components, it is preferable that
the reflection attenuation amount of the radio wave absorber is
high. Accordingly, the reflection attenuation amount of the radio
wave absorber may exceed the values exemplified above.
[0196] By the way, the on-vehicle radar, which has been attracting
attention in recent years, is a radar that uses radio waves in the
millimeter wave frequency band. The millimeter waves are
electromagnetic waves having a frequency of 30 GHz to 300 GHz. The
radio wave absorber preferably exhibits a transmission attenuation
amount and a reflection attenuation amount in the above respective
ranges with respect to a frequency of the radio wave, that is, one
or more frequencies in the frequency band of 3 terahertz (THz) or
less. From the viewpoint of usefulness for improving the
recognition accuracy of the on-vehicle radar, the frequency at
which the radio wave absorber exhibits a transmission attenuation
amount and a reflection attenuation amount in the above range is
preferably a millimeter wave frequency band, that is, one or more
frequencies in the frequency band of 30 GHz to 300 GHz, more
preferably one or more frequencies in the frequency band of 60 GHz
to 90 GHz, and still more preferably one or more frequencies in the
frequency band of 75 GHz to 85 GHz. As an example, the radio wave
absorber can be a radio wave absorber having a transmission
attenuation amount at a frequency of 76.5 GHz and a reflection
attenuation amount at a frequency of 76.5 GHz in the above
respective ranges. Such a radio wave absorber is suitable as a
radio wave absorber that is incorporated on a front side (an
incident side of the radio wave incident from the outside) of the
radio wave transmitting and receiving unit in the on-vehicle radar
in order to reduce the side lobe of the on-vehicle millimeter-wave
radar.
[0197] The "transmission attenuation amount" in the present
invention and the present specification is a value obtained by
measuring an S parameter in a measurement environment at an ambient
temperature of 15.degree. C. to 35.degree. C. with a free space
method by setting an incidence angle of 0.degree. and being
determined as S21 of the S parameter. The "reflection attenuation
amount" is a value determined as S11 of the S parameter by the same
measurement. The measurement can be carried out using a known
vector network analyzer and horn antenna. Examples of the specific
example of the measurement method include the methods described in
Examples described later.
[0198] By the way, in a radio wave absorber, a metal layer may be
laminated on a surface (a so-called back surface) opposite to the
surface on which radio waves are incident on the radio wave
absorber. Such a radio wave absorber is called a matching-type
radio wave absorber. In the matching-type radio wave absorber,
reflection attenuation characteristics can be enhanced by providing
a metal layer to utilize the phase difference absorption. On the
other hand, in one form, in the radio wave absorber, the radio wave
absorber itself can have excellent reflection attenuation
characteristics. Specifically, in one form, the radio wave absorber
can exhibit a high reflection attenuation amount regardless of the
metal layer. A radio wave absorber that is used without laminating
a metal layer on the back surface is generally called a
transmission-type radio wave absorber. In the conventional
transmission-type radio wave absorber containing a magnetic powder
and a binder, in general, the reflection attenuation amount tended
to decrease in a case where an attempt was made to increase the
transmission attenuation amount. On the other hand, in one form,
the radio wave absorber can exhibit a high reflection attenuation
amount and a high transmission attenuation amount regardless of the
metal layer.
[0199] The "metal layer" described in the present specification
means a layer containing a metal and substantially reflecting radio
waves. However, in a case where the radio wave absorber containing
a magnetic powder and a binder contains a metal, such a radio wave
absorber does not correspond to the metal layer. Here,
"substantially reflecting radio waves" means, for example,
reflecting 90% or more of incident radio waves in a case where the
radio waves are incident on the radio wave absorber in a state
where a metal layer is laminated on the back surface of the radio
wave absorber. Examples of the form of the metal layer include a
metal plate and a metal foil. For example, a metal layer formed on
the back surface of the radio wave absorber by vapor deposition can
be mentioned. In one form, the radio wave absorber can be used
without a metal layer being provided on the back surface. The fact
that the radio wave absorber can be used without a metal layer is
preferable from the viewpoint of recycling and the viewpoint of
cost. In addition, the quality of the radio wave absorber that is
used by laminating a metal layer on the back surface may
deteriorate due to the deterioration of the metal layer, the
peeling of the metal layer from the radio wave absorber. The fact
that it can be used without a metal layer being provided on the
back surface is also preferable in that such quality deterioration
does not occur.
EXAMPLES
[0200] Hereinafter, the present invention will be described based
on Examples. However, the present invention is not limited to
aspects described in Examples. Unless otherwise specified, steps
and evaluations described below were carried out in an environment
of an ambient temperature of 23.degree. C..+-.1.degree. C.
[0201] [Production of Magnetic Powder]
[0202] <Production of Magnetic Powder A-1 (Powder of
Substitution-Type Hexagonal Strontium Ferrite)>
[0203] A total amount of a raw material aqueous solution prepared
by dissolving 57.0 g of iron (III) chloride hexahydrate
[FeCl.sub.3.6H.sub.2O], 27.8 g of strontium chloride hexahydrate
[SrCl.sub.2.6H.sub.2O], and 10.7 g of aluminum chloride hexahydrate
[AlCl.sub.3.6H.sub.2O] in 216.0 g of water, and a total amount of a
solution prepared by adding 113.0 g of water to 181.3 g of an
aqueous solution of sodium hydroxide of a concentration of 5 mol/L
were added to 400.0 g of water kept at a temperature of 35.degree.
C. and stirred, respectively, at a flow rate of 10 mL/min and the
same timing, to obtain a first solution.
[0204] Next, after changing the solution temperature of the first
solution to be 25.degree. C., 24.7 g of an aqueous solution of
sodium hydroxide of a concentration of 1 mol/L was added while
maintaining this temperature to obtain a second solution. The pH of
the second solution was 9.0. The pH of the second solution was
measured using a desktop pH meter (F-71 manufactured by HORIBA,
Ltd.).
[0205] Next, the second solution was stirred for 15 minutes, and a
solution containing a reaction product which is a precursor of
magnetoplumbite-type hexagonal ferrite (a precursor-containing
solution) was obtained.
[0206] Next, the precursor-containing solution was subjected to the
centrifugal separation treatment [rotation speed: 3,000 rpm,
rotation time: 10 minutes] three times, and the obtained
precipitate was collected.
[0207] Next, the collected precipitate was dried in an oven at an
internal ambient temperature of 80.degree. C. for 12 hours to
obtain a precursor powder.
[0208] Next, the precursor powder was put in a muffle furnace, and
the temperature in the furnace was set to 1,100.degree. C. in an
ambient air atmosphere, followed by sintering for 4 hours, thereby
obtaining a sintered product.
[0209] Next, the obtained sintered product was pulverized for 90
seconds using a cutter mill pulverizer (Wonder Crusher WC-3
manufactured by Osaka Chemical Co., Ltd.) as the pulverizer, with
the variable speed dial of the pulverizer being set to "5"
(rotation speed: about 10,000 to 15,000 rpm).
[0210] As a result, a magnetic powder A-1 was obtained.
[0211] <Production of Magnetic Powders A-2 to A-7 (Powder of
Substitution-Type Hexagonal Strontium Ferrite)>
[0212] The same operation as in the production of the magnetic
powder A1 was carried out except that the pH of the second solution
was adjusted to the pH shown in Table 1 described later, to obtain
magnetic powders A-2 to A-7.
[0213] <Production of Magnetic Powder A-8 (Powder of
Unsubstitution-Type Hexagonal Strontium Ferrite)>
[0214] 15.02 g of strontium carbonate [SrCO.sub.3] and 90.24 g of
iron oxide [Fe.sub.2O.sub.3] were mixed and pulverized in an agate
mortar to obtain a powder of a precursor of the
magnetoplumbite-type hexagonal ferrite was.
[0215] Next, the precursor powder was put in a muffle furnace, and
the temperature in the furnace was set to 1,200.degree. C. in an
ambient air atmosphere, followed by sintering for 4 hours, thereby
obtaining a sintered product.
[0216] Next, the obtained sintered product was pulverized for 90
seconds using a cutter mill pulverizer (Wonder Crusher WC-3
manufactured by Osaka Chemical Co., Ltd.) as the pulverizer, with
the variable speed dial of the pulverizer being set to "5"
(rotation speed: about 10,000 to 15,000 rpm).
[0217] As a result, a magnetic powder A-8 was obtained.
[0218] <Checking of Crystal Structure>
[0219] The crystal structure of the magnetic material that
constitutes each of the above magnetic powders was checked by X-ray
diffraction analysis. As the measurement device, X'Pert Pro
manufactured by PANalytical Co., Ltd., which is a powder X-ray
diffractometer, was used. The measurement conditions are shown
below.
[0220] --Measurement Conditions--
[0221] X-ray source: CuK.alpha. ray
[0222] [Wavelength: 1.54 .ANG. (0.154 nm), output: 40 mA, 45
kV]
[0223] Scan range: 20.degree.<2.theta.<70.degree.
[0224] Scan interval: 0.05.degree.
[0225] Scan speed: 0.75.degree./min
[0226] As a result of the X-ray diffraction analysis, it was
confirmed that the magnetic powders A-1 to A-8 have a
magnetoplumbite-type crystal structure and are a single-phase
powder of a magnetoplumbite-type hexagonal ferrite that does not
include a crystal structure other than the magnetoplumbite-type
crystal structure.
[0227] <Checking of Constitution>
[0228] The constitution of the magnetic material that constitutes
each of the above magnetic powders was checked by high frequency
inductively coupled plasma emission spectroscopy. Specifically, the
checking was carried out by the following method.
[0229] A container beaker containing 12 mg of the magnetic powder
and 10 mL of an aqueous solution of hydrochloric acid of a
concentration of 4 mol/L was held on a hot plate at a set
temperature of 120.degree. C. for 3 hours to obtain a dissolution
solution. 30 mL of pure water was added to the obtained dissolution
solution, which is then filtered using a membrane filter having a
filter pore diameter of 0.1 .mu.m. Elemental analysis of the
filtrate obtained as described above was carried out using a high
frequency inductively coupled plasma emission spectrometer
[ICPS-8100, manufactured by Shimadzu Corporation]. Based on the
obtained elemental analysis results, a content of each atom with
respect to 100% by atom of iron atoms was obtained. Then, based on
the obtained content, the constitution of the magnetic material was
checked. As a result, it was confirmed that the constitutions of
the magnetic powders A-1 to A-7 were such that A in General Formula
1 is Sr and x is the value shown in Table 1. Further, it was
confirmed that the magnetic powder A-8 has a constitution of
SrFe.sub.12O.sub.19 (that is, it was an unsubstitution-type
strontium ferrite).
[0230] The resonance frequencies of the magnetic powders A-1 to A-7
were measured by the following method. The measurement results are
shown in Table 1.
[0231] (Method of Measuring Resonance Frequency)
[0232] Using each magnetic powder, a sheet sample for resonance
frequency measurement was produced by the following method.
[0233] 9.0 g of the magnetic powder, 1.05 g of the acrylonitrile
butadiene rubber (NBR) (JSR N215SL, manufactured by JSR
Corporation), and 6.1 g of cyclohexanone (a solvent) were stirred
and mixed with a stirring device [Awatori Neritaro ARE-310,
manufactured by Shinky Co., Ltd.], at a rotation speed of 2,000 rpm
for 5 minutes to prepare a composition for producing a sheet
sample.
[0234] Next, the prepared composition was applied onto a glass
plate (a support) using an applicator to form a coating film of the
above composition.
[0235] Next, the formed coating film was dried in an oven having an
internal ambient temperature of 80.degree. C. for 2 hours, and then
the sheet sample (thickness: 0.3 mm) was peeled off from the glass
plate.
[0236] Using the sheet sample obtained as described above, a vector
network analyzer (product name: N5225B) manufactured by Keysight
Technologies and a horn antenna (product name: RH12S23)
manufactured by KEYCOM Corp were used to measure an S parameter
according to the free space method by setting an incidence angle to
0.degree. and a sweep frequency to 60 GHz to 90 GHz. From this S
parameter, a peak frequency of permeability .mu.." of the imaginary
part was calculated using the Nicholson-Loss model method and this
peak frequency was used as the resonance frequency. The results are
shown in Table 1.
TABLE-US-00001 TABLE 1 Magnetic Magnetic Magnetic Magnetic Magnetic
Magnetic Magnetic powder A-1 powder A-2 powder A-3 powder A-4
powder A-5 powder A-6 powder A-7 pH of second 9.0 9.5 10.0 10.5
11.0 11.5 12.0 solution Value of x 2.35 2.28 2.21 2.14 2.00 1.87
1.80 Resonance 87.2 85.1 82.3 79.8 76.5 72.8 69.3 frequency
[GHz]
[0237] From the results shown in Table 1, it can be confirmed that
the value of x (that is, the A1 content) in General Formula 1 can
be controlled by adjusting the pH of the second solution.
Furthermore, it can be confirmed that the resonance frequency of
the magnetic powder can be controlled by controlling the A1
content. It can be said that the higher the resonance frequency of
the magnetic powder, the better the radio wave absorption
performance in the high frequency band.
[0238] <Production of Magnetic Powder R-1 Subjected to Surface
Treatment with Surface Treatment Agent>
[0239] 20 g of the magnetic powder A-1 obtained as described above
and 0.2 g of a surface treatment agent SP-3 (allyltrimethoxysilane)
were mixed for 60 seconds using a cutter mill pulverizer (Wonder
Crusher WC-3 manufactured by Osaka Chemical Co., Ltd.) with the
variable speed dial of the pulverizer being set to "3".
[0240] Next, the mixed powder was placed in an oven at a set
temperature of 90.degree. C. and dried by heating for 3 hours to
obtain a magnetic powder R-1 subjected to surface treatment with a
surface treatment agent.
[0241] <Production of Magnetic Powders R-2 to R-29 Subjected to
Surface Treatment with Surface Treatment Agent>
[0242] The same operation as in the production of the magnetic
powder R-1 was carried out except that the magnetic powder shown in
Table 2 was used and the using amount shown in Table 2 was used for
the surface treatment agent shown in Table 2, whereby magnetic
powders R-2 to R-29 subjected to surface treatment were
obtained.
[0243] Details of the magnetic powders R-1 to R-29 are shown in
Table 2 (Tables 2-1 to 2-3). The using amount of the surface
treatment agent in the table below is the amount with respect to
100 parts by mass of the magnetic powder subjected to surface
treatment.
TABLE-US-00002 TABLE 2-1 Magnetic powder subjected to surface
treatment R-1 R-2 R-3 R-4 R-5 R-6 R-7 R-8 R-9 R-10 Powder Kind A-1
A-2 A-3 A-4 A-5 A-6 A-7 A-5 A-5 A-5 Surface Kind SP-3 SP-3 SP-3
SP-3 SP-3 SP-3 SP-3 SK-1 SK-2 SK-3 treatment Using amount 1.0 1.0
1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 agent [part by mass]
TABLE-US-00003 TABLE 2-2 Magnetic powder subjected to surface
treatment R-11 R-12 R-13 R-14 R-15 R-16 R-17 R-18 R-19 R-20 Powder
Kind A-5 A-5 A-5 A-5 A-5 A-5 A-5 A-5 A-5 A-5 Surface Kind SV-1 SV-2
SV-3 SV-4 SV-5 SP-1 SP-2 SP-4 SI-1 SI-2 treatment Using amount 1.0
1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 agent [part by mass]
TABLE-US-00004 TABLE 2-3 Magnetic powder subjected to surface
treatment R-21 R-22 R-23 R-24 R-25 R-26 R-27 R-28 R-29 Powder Kind
A-5 A-5 A-5 A-5 A-5 A-5 A-5 A-8 A-5 Surface Kind SI-3 SP-3 SP-3
SP-3 SP-3 SP-3 SP-3 SP-3 ST-1 treatment Using amount 1.0 0.2 0.5
1.5 2.0 5.0 10.0 1.0 1.0 agent [part by mass]
[0244] The surface treatment agents in Table 2 are the following
surface treatment agents.
[0245] [Surface Treatment Agent]
[0246] SK-1: Allyltrimethoxysilane (SIA0540.0 manufactured by
Gelest Inc.)
[0247] SK-2: Phenethyldimethoxysilane (SIP6722.6 manufactured by
Gelest Inc.)
[0248] SK-3: [2-(3-cyclohexenyl)ethyl]trimethoxysilane (SIC2460.0
manufactured by Gelest Inc.)
[0249] SV-1: Vinyl trimethoxysilane (KBM-1003 manufactured by
Shin-Etsu Chemical Co., Ltd.)
[0250] SV-2: 7-octenyltrimethoxysilane (KBM-1083 manufactured by
Shin-Etsu Chemical Co., Ltd.)
[0251] SV-3: (3-methacryloxypropyl)trimethoxysilane (SIM6487.4
manufactured by Gelest Inc.)
[0252] SV-4: 8-methacryloxyoctyltrimethoxysilane (KBM-5803
manufactured by Shin-Etsu Chemical Co., Ltd.)
[0253] SV-5: 3-acrylamide propyltrimethoxysilane (SIA0146.0
manufactured by Gelest Inc.)
[0254] SP-1: 3-glycidylpropyltrimethoxysilane (SIG5840.0
manufactured by Gelest Inc.)
[0255] SP-2: 5,6-epoxyhexyltriethoxysilane (SIE4675.0 manufactured
by Gelest Inc.)
[0256] SP-3: 8-glycidoxyoctyltrimethoxysilane (KBM-4803
manufactured by Shin-Etsu Chemical Co., Ltd.)
[0257] SP-4: 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane
(SIE4670.0 manufactured by Gelest Inc.)
[0258] SI-1: Polydimethylsiloxane (DMS-T21 manufactured by Gelest
Inc., weight-average molecular weight: 5,970)
[0259] SI-2: A polyalkylene oxide-modified silicone (DBE-621
manufactured by Gelest Inc., ethylene oxide content: 50%,
weight-average molecular weight: 2,500)
[0260] SI-3: A hydrogen-terminated polydimethylsiloxane (DMS-H21
manufactured by Gelest Inc., weight-average molecular weight:
6,000)
[0261] ST-1: Tristearoyl isopropyl titanate (manufactured by AIM
Co., Ltd.)
[0262] [Production of Radio Wave Absorber]
Example 1
[0263] 3.0 g of the magnetic powder R-1, 2.0 g of the olefin-based
resin B-1 (the ethylene-vinyl acetate-maleic acid anhydride resin),
and 0.05 g of a hindered phenol compound (Irganox 1330 manufactured
by BASF SE) as an antioxidant were introduced into a kneader (Labo
Plastomill Micro manufactured by Toyo Seiki Co., Ltd.) at a set
temperature of 160.degree. C., mixed, and kneaded at a rotor
rotation speed of 100 rpm for 5 minutes to obtain an aggregated
kneaded material.
[0264] The obtained aggregated kneaded material was subjected to
press molding using a heating press machine (heating temperature:
150.degree. C., press time: 1 minute, pressure: 20 MPa) to produce
a radio wave absorber (a radio wave absorbing sheet) having a
length of 10.0 cm, a width of 10.0 cm, and a thickness 2.0 mm.
Examples 2 to 36
[0265] The same operation as in Example 1 was carried out except
that a magnetic powder shown in Table 3 was used as the magnetic
powder subjected to surface treatment with a surface treatment
agent and an olefin-based resin shown in Table 3 was used, whereby
a radio wave absorber (a radio wave absorbing sheet) was
produced.
Examples 37 to 40
[0266] Regarding the content of the magnetic powder and the
olefin-based resin in the mixture for preparing the kneaded
material of Example 1, the magnetic powder is 60% by mass, and the
olefin-based resin is 40% by mass, with respect to the total mass
of the magnetic powder and the olefin-based resin. In Examples 37
to 40, the same operation as in Example 1 was carried out except
that the contents of the magnetic powder and the olefin-based resin
were changed as shown in Table 3, whereby a radio wave absorber (a
radio wave absorbing sheet) was produced.
Comparative Example 1
[0267] The same operation as in Example 1 was carried out except
that the magnetic powder R-1 was not used, whereby a sheet made of
an olefin-based resin was produced.
Comparative Examples 2 and 3
[0268] The same operation as in Example 1 was carried out except
that a magnetic powder (subjected to no surface treatment) shown in
Table 3 was used as the magnetic powder, whereby a radio wave
absorber (a radio wave absorbing sheet) was produced.
Comparative Example 4
[0269] The same operation as in Example 1 was carried out except
that the magnetic powder (the powder of the unsubstitution-type
hexagonal ferrite subjected to surface treatment with a surface
treatment agent) shown in Table 3 was used as the magnetic powder,
whereby a radio wave absorber (a radio wave absorbing sheet) was
produced.
Comparative Example 5
[0270] The same operation as in Example 1 was carried out except
that a magnetic powder R-29 subjected to surface treatment with a
titanium-based compound ST-1 was used, whereby a radio wave
absorber (a radio wave absorbing sheet) was produced.
[0271] In each of Examples and Comparative Examples described
above, a plurality of sheets were produced, and each of the sheets
was used for each of the following evaluations.
[0272] [Evaluation method]
[0273] (1) Radio Wave Absorption Performance
[0274] The transmission attenuation amount (unit: dB) and the
reflection attenuation amount (unit: dB) of each of the sheets of
Examples and Comparative Examples were measured by the following
method.
[0275] As the measurement device, a vector network analyzer
(product name: N5225B) manufactured by Keysight Technologies and a
horn antenna (product name: RH12S23) manufactured by KEYCOM Corp.
were used to measure an S parameter with a free space method by
setting an incidence angle to 0.degree. and a sweep frequency to 60
GHz to 90 GHz, with one plane of each of the sheets being directed
toward the incident side, S21 of the S parameter at a frequency of
76.5 GHz was taken as the transmission attenuation amount, and S11
of the S parameter at a frequency of 76.5 GHz was taken as the
reflection attenuation amount.
[0276] From the measured values, the radio wave absorption
performance was evaluated according to the following standards.
[0277] (Evaluation Standards)
[0278] A: Both transmission attenuation amount and reflection
attenuation amount are 10.0 dB or more.
[0279] B: Both transmission attenuation amount and reflection
attenuation amount are 8.0 dB or more and less than 10.0 dB.
[0280] C: Both transmission attenuation amount and reflection
attenuation amount are 6.0 dB or more and less than 8.0 dB.
[0281] D: Both transmission attenuation amount and reflection
attenuation amount are less than 6.0 dB.
[0282] (2) Vibration Damping Property (Loss Coefficient)
[0283] A specimen having a length of 10.0 cm, a width of 1.27 cm,
and a thickness of 2.0 mm was cut out from each of the sheets of
Examples and Comparative Examples and subjected to the measurement
in a temperature range of 0.degree. C. to 80.degree. C., and the
value of the loss coefficient at 23.degree. C. was calculated,
according to the half-width method, from the peak of the
second-order resonance of the frequency response function, which
had been measured by the central vibration method based on JIS
K7391: 2008. For the measurement, a system consisting of an
oscillator of Type 3160, an amplifier of Type 2718, an exciter of
Type 4810, and an acceleration sensor of Type 8001 was used (all
manufactured by Bruel & Kjer), and a loss coefficient
measurement software MS18143 installed in the above system was used
to calculate the loss coefficient. The vibration damping property
was evaluated according to the following standards.
[0284] (Evaluation Standards)
[0285] A: Loss coefficient is 0.12 or more.
[0286] B: Loss coefficient is 0.10 or more and less than 0.12.
[0287] C: Loss coefficient is 0.08 or more and less than 0.10.
[0288] D: Loss coefficient is less than 0.08.
[0289] (3) Weather Fastness
[0290] Each of the sheets of Examples and Comparative Examples was
charged into a weather fastness tester (Super Xenon Weather Meter
SX75 manufactured by Suga Test Instruments Co., Ltd.), the sheet
surface was irradiated with light under the light irradiation
conditions of the weather fastness tester were set to an
illuminance of 180 W/m.sup.2 and a black panel temperature
63.degree. C. with humidification and rainfall, and then the hue
change of the sheet surface irradiated with light for 50 hours was
evaluated with the color difference value .DELTA.E obtained using a
color difference meter (CR-400 manufactured by Konica Minolta
Inc.). From the .DELTA.E value, the weather fastness was evaluated
according to the following standards.
[0291] (Evaluation Standards)
[0292] A: The .DELTA.E value before and after irradiation is less
than 1.0.
[0293] B: The .DELTA.E value before and after irradiation is 1.0 or
more and less than 2.5.
[0294] C: The .DELTA.E value before and after irradiation is 2.5 or
more and less than 5.0.
[0295] D: The .DELTA.E value before and after irradiation is 5.0 or
more.
[0296] The above results are shown in Table 3 (Tables 3-1 to
3-6).
TABLE-US-00005 TABLE 3-1 Example Example Example Example Example
Example Example Example Example Example 1 2 3 4 5 6 7 8 9 10
Magnetic Kind R-1 R-2 R-3 R-4 R-5 R-6 R-7 R-8 R-9 R-10 powder
Surface Kind SP-3 SP-3 SP-3 SP-3 SP-3 SP-3 SP-3 SK-1 SK-2 SK-3
treatment Using 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 agent
amount [part by mass] Content [% by mass] 60 60 60 60 60 60 60 60
60 60 Binder Kind B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 Content
[% by mass] 40 40 40 40 40 40 40 40 40 40 Radio wave absorption
performance A A A A A A A B B B Vibration damping property A A A A
A A A A A A Weather fastness A A A A A A A B A B
TABLE-US-00006 TABLE 3-2 Example Example Example Example Example
Example Example Example Example Example 11 12 13 14 15 16 17 18 19
20 Magnetic Kind R-11 R-12 R-13 R-14 R-15 R-16 R-17 R-18 R-19 R-20
powder Surface Kind SV-1 SV-2 SV-3 SV-4 SV-5 SP-1 SP-2 SP-4 SI-1
SI-2 treatment Using 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 agent
amount [part by mass] Content [% by mass] 60 60 60 60 60 60 60 60
60 60 Binder Kind B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-1 Content
[% by mass] 40 40 40 40 40 40 40 40 40 40 Radio wave absorption
performance B B B B B A A A C B Vibration damping property A A A A
A A A A C C Weather fastness B A B B B A A A B B
TABLE-US-00007 TABLE 3-3 Example Example Example Example Example
Example Example Example Example Example 21 22 23 24 25 26 27 28 29
30 Magnetic Kind R-21 R-22 R-23 R-24 R-25 R-26 R-27 R-5 R-5 R-5
powder Surface Kind SI-3 SP-3 SP-3 SP-3 SP-3 SP-3 SP-3 SP-3 SP-3
SP-3 treatment Using 1.0 0.2 0.5 1.5 2.0 5.0 10.0 1.0 1.0 1.0 agent
amount [part by mass] Content [% by mass] 60 60 60 60 60 60 60 60
60 60 Binder Kind B-1 B-1 B-1 B-1 B-1 B-1 B-1 B-2 B-3 B-4 Content
[% by mass] 40 40 40 40 40 40 40 40 40 40 Radio wave absorption
performance B C A A A B B A A A Vibration damping property C B A A
B B C A A A Weather fastness B C A A A A A A A A
TABLE-US-00008 TABLE 3-4 Example Example Example Example Example
Example 31 32 33 34 35 36 Magnetic Kind R-5 R-5 R-5 R-5 R-5 R-5
powder Surface Kind SP-3 SP-3 SP-3 SP-3 SP-3 SP-3 treatment Using
1.0 1.0 1.0 1.0 1.0 1.0 agent amount [part by mass] Content [% by
mass] 60 60 60 60 60 60 Binder Kind B-5 B-6 B-7 B-8 B-9 B-10
Content [% by mass] 40 40 40 40 40 40 Radio wave absorption
performance A A A B B B Vibration damping property A A A A A A
Weather fastness A A A B B C
TABLE-US-00009 TABLE 3-5 Exam- Exam- Exam- Exam- ple ple ple ple 37
38 39 40 Magnetic Kind R-5 R-5 R-5 R-5 powder Surface Kind SP-3
SP-3 SP-3 SP-3 treatment Using 1.0 1.0 1.0 1.0 agent amount [part
by mass] Content [% by mass] 20 40 70 80 Binder Kind B-1 B-1 B-1
B-1 Content [% by mass] 80 60 30 20 Radio wave absorption C B A A
performance Vibration damping property A A A A Weather fastness A A
A B
TABLE-US-00010 TABLE 3-6 Comparative Comparative Comparative
Comparative Comparative Example 1 Example 2 Example 3 Example 4
Example 5 Magnetic Kind -- A-5 A-8 R-28 R-29 powder Surface Kind --
-- SP-3 ST-1 treatment Using 1 1.0 agent amount [part by mass]
Content [% by mass] 60 60 60 60 Binder Kind B-1 B-1 B-1 B-1 B-1
Content [% by mass] 100 40 40 40 40 Radio wave absorption
performance D C D D C Vibration damping property C D D C D Weather
fastness D D D D D
[0297] The binders in Table 3 are the following olefin-based
resins.
[0298] [Binder]
[0299] B-1: A ethylene-vinyl acetate-maleic acid anhydride resin
(OREVAC T 9314 manufactured by Arkema S.A.)
[0300] B-2: A maleic acid anhydride graft-polyethylene resin
(OREVAC G OE808 manufactured by Arkema S.A.)
[0301] B-3: An ethylene-acrylic acid ester-maleic acid anhydride
resin (BONDINE 5500 manufactured by Arkema S.A.)
[0302] B-4: A cycloolefin resin (manufactured by ZEON CORPORATION,
trade name: "ZEONOR 1020R")
[0303] B-5: Polymethylpentene (TPX RT18 manufactured by Mitsui
Chemicals, Inc.)
[0304] B-6: An ethylene-norbornene resin (Topas 8007S-04
manufactured by Polyplastics Co., Ltd.)
[0305] B-7: A dicyclopentadiene resin (METTON T02 manufactured by
RIMTEC Corporation)
[0306] B-8: An ethylene-vinyl acetate resin (EVA; Ultrathene 537
manufactured by Tosoh Corporation)
[0307] B-9: A high-density polyethylene resin (HDPE; HI-ZEX 232J
manufactured by Prime Polymer Co., Ltd.)
[0308] B-10: polypropylene (PP; NOVATEC MA3 manufactured by Japan
Polypropylene Corporation)
[0309] The radio wave absorbers of Examples 1 to 40 contain a
powder of a substitution-type hexagonal ferrite subjected to
surface treatment with a silicon-based compound, as a magnetic
powder, and contain an olefin-based resin as a binder.
[0310] On the other hand, the radio wave absorber of Comparative
Example 2 contains a powder of a substitution-type hexagonal
ferrite subjected to no surface treatment and an olefin-based
resin, the radio wave absorber of Comparative Example 3 contains a
powder of an unsubstitution-type hexagonal ferrite subjected to no
surface treatment and an olefin-based resin, and the radio wave
absorber of Comparative Example 4 contains a powder of an
unsubstitution-type hexagonal ferrite subjected to surface
treatment with a silicon-based compound and an olefin-based resin.
The radio wave absorber of Comparative Example 5 contains a powder
of a substitution-type hexagonal ferrite subjected to surface
treatment with a titanium-based compound, and an olefin-based
resin.
[0311] From the comparison between Examples 1 to 40 in Table 3 and
Comparative Examples 2 to 5, it can be confirmed in a case where a
substitution-type hexagonal ferrite powder subjected to surface
treatment with a silicon-based compound and an olefin-based resin
are combined as a magnetic powder and a binder, it is possible to
obtain a radio wave absorber excellent radio wave absorption
performance, weather fastness, and vibration damping property.
[0312] One embodiment of the present invention is useful in the
technical field of carrying out various automatic driving controls
such as automatic driving control of an automobile.
* * * * *